[roundup.git] / doc / design.txt

========================================================
Roundup - An Issue-Tracking System for Knowledge Workers
========================================================

:Authors: Ka-Ping Yee (original__), Richard Jones (implementation)

__ spec.html

.. contents::

Introduction
---------------

This document presents a description of the components
of the Roundup system and specifies their interfaces and
behaviour in sufficient detail to guide an implementation.
For the philosophy and rationale behind the Roundup design,
see the first-round Software Carpentry submission for Roundup.
This document fleshes out that design as well as specifying
interfaces so that the components can be developed separately.


The Layer Cake
-----------------

Lots of software design documents come with a picture of
a cake.  Everybody seems to like them.  I also like cakes
(i think they are tasty).  So i, too, shall include
a picture of a cake here::

     _________________________________________________________________________
    |  E-mail Client   |   Web Browser   |   Detector Scripts   |    Shell    |
    |------------------+-----------------+----------------------+-------------|
    |   E-mail User    |    Web User     |      Detector        |   Command   | 
    |-------------------------------------------------------------------------|
    |                         Roundup Database Layer                          |
    |-------------------------------------------------------------------------|
    |                          Hyperdatabase Layer                            |
    |-------------------------------------------------------------------------|
    |                             Storage Layer                               |
     -------------------------------------------------------------------------

The colourful parts of the cake are part of our system;
the faint grey parts of the cake are external components.

I will now proceed to forgo all table manners and
eat from the bottom of the cake to the top.  You may want
to stand back a bit so you don't get covered in crumbs.


Hyperdatabase
-------------

The lowest-level component to be implemented is the hyperdatabase.
The hyperdatabase is intended to be
a flexible data store that can hold configurable data in
records which we call nodes.

The hyperdatabase is implemented on top of the storage layer,
an external module for storing its data.  The storage layer could
be a third-party RDBMS; for a "batteries-included" distribution,
implementing the hyperdatabase on the standard bsddb
module is suggested.

Dates and Date Arithmetic
~~~~~~~~~~~~~~~~~~~~~~~~~

Before we get into the hyperdatabase itself, we need a
way of handling dates.  The hyperdatabase module provides
Timestamp objects for
representing date-and-time stamps and Interval objects for
representing date-and-time intervals.

As strings, date-and-time stamps are specified with
the date in international standard format
(``yyyy-mm-dd``)
joined to the time (``hh:mm:ss``)
by a period "``.``".  Dates in
this form can be easily compared and are fairly readable
when printed.  An example of a valid stamp is
"``2000-06-24.13:03:59``".
We'll call this the "full date format".  When Timestamp objects are
printed as strings, they appear in the full date format with
the time always given in GMT.  The full date format is always
exactly 19 characters long.

For user input, some partial forms are also permitted:
the whole time or just the seconds may be omitted; and the whole date
may be omitted or just the year may be omitted.  If the time is given,
the time is interpreted in the user's local time zone.
The Date constructor takes care of these conversions.
In the following examples, suppose that ``yyyy`` is the current year,
``mm`` is the current month, and ``dd`` is the current
day of the month; and suppose that the user is on Eastern Standard Time.

-   "2000-04-17" means <Date 2000-04-17.00:00:00>
-   "01-25" means <Date yyyy-01-25.00:00:00>
-   "2000-04-17.03:45" means <Date 2000-04-17.08:45:00>
-   "08-13.22:13" means <Date yyyy-08-14.03:13:00>
-   "11-07.09:32:43" means <Date yyyy-11-07.14:32:43>
-   "14:25" means
-   <Date yyyy-mm-dd.19:25:00>
-   "8:47:11" means
-   <Date yyyy-mm-dd.13:47:11>
-   the special date "." means "right now"


Date intervals are specified using the suffixes
"y", "m", and "d".  The suffix "w" (for "week") means 7 days.
Time intervals are specified in hh:mm:ss format (the seconds
may be omitted, but the hours and minutes may not).

-   "3y" means three years
-   "2y 1m" means two years and one month
-   "1m 25d" means one month and 25 days
-   "2w 3d" means two weeks and three days
-   "1d 2:50" means one day, two hours, and 50 minutes
-   "14:00" means 14 hours
-   "0:04:33" means four minutes and 33 seconds


The Date class should understand simple date expressions of the form 
*stamp* ``+`` *interval* and *stamp* ``-`` *interval*.
When adding or subtracting intervals involving months or years, the
components are handled separately.  For example, when evaluating
"``2000-06-25 + 1m 10d``", we first add one month to
get 2000-07-25, then add 10 days to get
2000-08-04 (rather than trying to decide whether
1m 10d means 38 or 40 or 41 days).

Here is an outline of the Date and Interval classes::

    class Date:
        def __init__(self, spec, offset):
            """Construct a date given a specification and a time zone offset.

            'spec' is a full date or a partial form, with an optional
            added or subtracted interval.  'offset' is the local time
            zone offset from GMT in hours.
            """

        def __add__(self, interval):
            """Add an interval to this date to produce another date."""

        def __sub__(self, interval):
            """Subtract an interval from this date to produce another date."""

        def __cmp__(self, other):
            """Compare this date to another date."""

        def __str__(self):
            """Return this date as a string in the yyyy-mm-dd.hh:mm:ss format."""

        def local(self, offset):
            """Return this date as yyyy-mm-dd.hh:mm:ss in a local time zone."""

    class Interval:
        def __init__(self, spec):
            """Construct an interval given a specification."""

        def __cmp__(self, other):
            """Compare this interval to another interval."""
            
        def __str__(self):
            """Return this interval as a string."""



Here are some examples of how these classes would behave in practice.
For the following examples, assume that we are on Eastern Standard
Time and the current local time is 19:34:02 on 25 June 2000::

    >>> Date(".")
    <Date 2000-06-26.00:34:02>
    >>> _.local(-5)
    "2000-06-25.19:34:02"
    >>> Date(". + 2d")
    <Date 2000-06-28.00:34:02>
    >>> Date("1997-04-17", -5)
    <Date 1997-04-17.00:00:00>
    >>> Date("01-25", -5)
    <Date 2000-01-25.00:00:00>
    >>> Date("08-13.22:13", -5)
    <Date 2000-08-14.03:13:00>
    >>> Date("14:25", -5)
    <Date 2000-06-25.19:25:00>
    >>> Interval("  3w  1  d  2:00")
    <Interval 22d 2:00>
    >>> Date(". + 2d") - Interval("3w")
    <Date 2000-06-07.00:34:02>

Nodes and Classes
~~~~~~~~~~~~~~~~~

Nodes contain data in properties.  To Python, these
properties are presented as the key-value pairs of a dictionary.
Each node belongs to a class which defines the names
and types of its properties.  The database permits the creation
and modification of classes as well as nodes.

Identifiers and Designators
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Each node has a numeric identifier which is unique among
nodes in its class.  The nodes are numbered sequentially
within each class in order of creation, starting from 1.
The designator
for a node is a way to identify a node in the database, and
consists of the name of the node's class concatenated with
the node's numeric identifier.

For example, if "spam" and "eggs" are classes, the first
node created in class "spam" has id 1 and designator "spam1".
The first node created in class "eggs" also has id 1 but has
the distinct designator "eggs1".  Node designators are
conventionally enclosed in square brackets when mentioned
in plain text.  This permits a casual mention of, say,
"[patch37]" in an e-mail message to be turned into an active
hyperlink.

Property Names and Types
~~~~~~~~~~~~~~~~~~~~~~~~

Property names must begin with a letter.

A property may be one of five basic types:

- String properties are for storing arbitrary-length strings.

- Boolean properties are for storing true/false, or yes/no values.

- Number properties are for storing numeric values.

- Date properties store date-and-time stamps.
  Their values are Timestamp objects.

- A Link property refers to a single other node
  selected from a specified class.  The class is part of the property;
  the value is an integer, the id of the chosen node.

- A Multilink property refers to possibly many nodes
  in a specified class.  The value is a list of integers.

*None* is also a permitted value for any of these property
types.  An attempt to store None into a Multilink property stores an empty list.

A property that is not specified will return as None from a *get*
operation.

Hyperdb Interface Specification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The hyperdb module provides property objects to designate
the different kinds of properties.  These objects are used when
specifying what properties belong in classes::

    class String:
        def __init__(self, indexme='no'):
            """An object designating a String property."""

    class Boolean:
        def __init__(self):
            """An object designating a Boolean property."""

    class Number:
        def __init__(self):
            """An object designating a Number property."""

    class Date:
        def __init__(self):
            """An object designating a Date property."""

    class Link:
        def __init__(self, classname, do_journal='yes'):
            """An object designating a Link property that links to
            nodes in a specified class.

            If the do_journal argument is not 'yes' then changes to
            the property are not journalled in the linked node.
            """

    class Multilink:
        def __init__(self, classname, do_journal='yes'):
            """An object designating a Multilink property that links
            to nodes in a specified class.

            If the do_journal argument is not 'yes' then changes to
            the property are not journalled in the linked node(s).
            """


Here is the interface provided by the hyperdatabase::

    class Database:
        """A database for storing records containing flexible data types."""

        def __init__(self, storagelocator, journaltag):
            """Open a hyperdatabase given a specifier to some storage.

            The meaning of 'storagelocator' depends on the particular
            implementation of the hyperdatabase.  It could be a file name,
            a directory path, a socket descriptor for a connection to a
            database over the network, etc.

            The 'journaltag' is a token that will be attached to the journal
            entries for any edits done on the database.  If 'journaltag' is
            None, the database is opened in read-only mode: the Class.create(),
            Class.set(), and Class.retire() methods are disabled.
            """

        def __getattr__(self, classname):
            """A convenient way of calling self.getclass(classname)."""

        def getclasses(self):
            """Return a list of the names of all existing classes."""

        def getclass(self, classname):
            """Get the Class object representing a particular class.

            If 'classname' is not a valid class name, a KeyError is raised.
            """

    class Class:
        """The handle to a particular class of nodes in a hyperdatabase."""

        def __init__(self, db, classname, **properties):
            """Create a new class with a given name and property specification.

            'classname' must not collide with the name of an existing class,
            or a ValueError is raised.  The keyword arguments in 'properties'
            must map names to property objects, or a TypeError is raised.
            """

        # Editing nodes:

        def create(self, **propvalues):
            """Create a new node of this class and return its id.

            The keyword arguments in 'propvalues' map property names to values.
            The values of arguments must be acceptable for the types of their
            corresponding properties or a TypeError is raised.  If this class
            has a key property, it must be present and its value must not
            collide with other key strings or a ValueError is raised.  Any other
            properties on this class that are missing from the 'propvalues'
            dictionary are set to None.  If an id in a link or multilink
            property does not refer to a valid node, an IndexError is raised.
            """

        def get(self, nodeid, propname):
            """Get the value of a property on an existing node of this class.

            'nodeid' must be the id of an existing node of this class or an
            IndexError is raised.  'propname' must be the name of a property
            of this class or a KeyError is raised.
            """

        def set(self, nodeid, **propvalues):
            """Modify a property on an existing node of this class.
            
            'nodeid' must be the id of an existing node of this class or an
            IndexError is raised.  Each key in 'propvalues' must be the name
            of a property of this class or a KeyError is raised.  All values
            in 'propvalues' must be acceptable types for their corresponding
            properties or a TypeError is raised.  If the value of the key
            property is set, it must not collide with other key strings or a
            ValueError is raised.  If the value of a Link or Multilink
            property contains an invalid node id, a ValueError is raised.
            """

        def retire(self, nodeid):
            """Retire a node.
            
            The properties on the node remain available from the get() method,
            and the node's id is never reused.  Retired nodes are not returned
            by the find(), list(), or lookup() methods, and other nodes may
            reuse the values of their key properties.
            """

        def history(self, nodeid):
            """Retrieve the journal of edits on a particular node.

            'nodeid' must be the id of an existing node of this class or an
            IndexError is raised.

            The returned list contains tuples of the form

                (date, tag, action, params)

            'date' is a Timestamp object specifying the time of the change and
            'tag' is the journaltag specified when the database was opened.
            'action' may be:

                'create' or 'set' -- 'params' is a dictionary of property values
                'link' or 'unlink' -- 'params' is (classname, nodeid, propname)
                'retire' -- 'params' is None
            """

        # Locating nodes:

        def setkey(self, propname):
            """Select a String property of this class to be the key property.

            'propname' must be the name of a String property of this class or
            None, or a TypeError is raised.  The values of the key property on
            all existing nodes must be unique or a ValueError is raised.
            """

        def getkey(self):
            """Return the name of the key property for this class or None."""

        def lookup(self, keyvalue):
            """Locate a particular node by its key property and return its id.

            If this class has no key property, a TypeError is raised.  If the
            'keyvalue' matches one of the values for the key property among
            the nodes in this class, the matching node's id is returned;
            otherwise a KeyError is raised.
            """

        def find(self, propname, nodeid):
            """Get the ids of nodes in this class which link to a given node.
            
            'propname' must be the name of a property in this class, or a
            KeyError is raised.  That property must be a Link or Multilink
            property, or a TypeError is raised.  'nodeid' must be the id of
            an existing node in the class linked to by the given property,
            or an IndexError is raised.
            """

        def list(self):
            """Return a list of the ids of the active nodes in this class."""

        def count(self):
            """Get the number of nodes in this class.

            If the returned integer is 'numnodes', the ids of all the nodes
            in this class run from 1 to numnodes, and numnodes+1 will be the
            id of the next node to be created in this class.
            """

        # Manipulating properties:

        def getprops(self):
            """Return a dictionary mapping property names to property objects."""

        def addprop(self, **properties):
            """Add properties to this class.

            The keyword arguments in 'properties' must map names to property
            objects, or a TypeError is raised.  None of the keys in 'properties'
            may collide with the names of existing properties, or a ValueError
            is raised before any properties have been added.
            """

TODO: additional methods

Hyperdatabase Implementations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Hyperdatabase implementations exist to create the interface described in the
`hyperdb interface specification`_
over an existing storage mechanism. Examples are relational databases,
\*dbm key-value databases, and so on.

TODO: finish


Application Example
~~~~~~~~~~~~~~~~~~~

Here is an example of how the hyperdatabase module would work in practice::

    >>> import hyperdb
    >>> db = hyperdb.Database("foo.db", "ping")
    >>> db
    <hyperdb.Database "foo.db" opened by "ping">
    >>> hyperdb.Class(db, "status", name=hyperdb.String())
    <hyperdb.Class "status">
    >>> _.setkey("name")
    >>> db.status.create(name="unread")
    1
    >>> db.status.create(name="in-progress")
    2
    >>> db.status.create(name="testing")
    3
    >>> db.status.create(name="resolved")
    4
    >>> db.status.count()
    4
    >>> db.status.list()
    [1, 2, 3, 4]
    >>> db.status.lookup("in-progress")
    2
    >>> db.status.retire(3)
    >>> db.status.list()
    [1, 2, 4]
    >>> hyperdb.Class(db, "issue", title=hyperdb.String(), status=hyperdb.Link("status"))
    <hyperdb.Class "issue">
    >>> db.issue.create(title="spam", status=1)
    1
    >>> db.issue.create(title="eggs", status=2)
    2
    >>> db.issue.create(title="ham", status=4)
    3
    >>> db.issue.create(title="arguments", status=2)
    4
    >>> db.issue.create(title="abuse", status=1)
    5
    >>> hyperdb.Class(db, "user", username=hyperdb.Key(), password=hyperdb.String())
    <hyperdb.Class "user">
    >>> db.issue.addprop(fixer=hyperdb.Link("user"))
    >>> db.issue.getprops()
    {"title": <hyperdb.String>, "status": <hyperdb.Link to "status">,
     "user": <hyperdb.Link to "user">}
    >>> db.issue.set(5, status=2)
    >>> db.issue.get(5, "status")
    2
    >>> db.status.get(2, "name")
    "in-progress"
    >>> db.issue.get(5, "title")
    "abuse"
    >>> db.issue.find("status", db.status.lookup("in-progress"))
    [2, 4, 5]
    >>> db.issue.history(5)
    [(<Date 2000-06-28.19:09:43>, "ping", "create", {"title": "abuse", "status": 1}),
     (<Date 2000-06-28.19:11:04>, "ping", "set", {"status": 2})]
    >>> db.status.history(1)
    [(<Date 2000-06-28.19:09:43>, "ping", "link", ("issue", 5, "status")),
     (<Date 2000-06-28.19:11:04>, "ping", "unlink", ("issue", 5, "status"))]
    >>> db.status.history(2)
    [(<Date 2000-06-28.19:11:04>, "ping", "link", ("issue", 5, "status"))]


For the purposes of journalling, when a Multilink property is
set to a new list of nodes, the hyperdatabase compares the old
list to the new list.
The journal records "unlink" events for all the nodes that appear
in the old list but not the new list,
and "link" events for
all the nodes that appear in the new list but not in the old list.


Roundup Database
----------------

The Roundup database layer is implemented on top of the
hyperdatabase and mediates calls to the database.
Some of the classes in the Roundup database are considered
issue classes.
The Roundup database layer adds detectors and user nodes,
and on issues it provides mail spools, nosy lists, and superseders.

TODO: where functionality is implemented.

Reserved Classes
~~~~~~~~~~~~~~~~

Internal to this layer we reserve three special classes
of nodes that are not issues.

Users
""""""""""""

Users are stored in the hyperdatabase as nodes of
class "user".  The "user" class has the definition::

    hyperdb.Class(db, "user", username=hyperdb.String(),
                              password=hyperdb.String(),
                              address=hyperdb.String())
    db.user.setkey("username")

Messages
"""""""""""""""

E-mail messages are represented by hyperdatabase nodes of class "msg".
The actual text content of the messages is stored in separate files.
(There's no advantage to be gained by stuffing them into the
hyperdatabase, and if messages are stored in ordinary text files,
they can be grepped from the command line.)  The text of a message is
saved in a file named after the message node designator (e.g. "msg23")
for the sake of the command interface (see below).  Attachments are
stored separately and associated with "file" nodes.
The "msg" class has the definition::

    hyperdb.Class(db, "msg", author=hyperdb.Link("user"),
                             recipients=hyperdb.Multilink("user"),
                             date=hyperdb.Date(),
                             summary=hyperdb.String(),
                             files=hyperdb.Multilink("file"))

The "author" property indicates the author of the message
(a "user" node must exist in the hyperdatabase for any messages
that are stored in the system).
The "summary" property contains a summary of the message for display
in a message index.

Files
""""""""""""

Submitted files are represented by hyperdatabase
nodes of class "file".  Like e-mail messages, the file content
is stored in files outside the database,
named after the file node designator (e.g. "file17").
The "file" class has the definition::

    hyperdb.Class(db, "file", user=hyperdb.Link("user"),
                              name=hyperdb.String(),
                              type=hyperdb.String())

The "user" property indicates the user who submitted the
file, the "name" property holds the original name of the file,
and the "type" property holds the MIME type of the file as received.

Issue Classes
~~~~~~~~~~~~~

All issues have the following standard properties:

=========== ==========================
Property    Definition
=========== ==========================
title       hyperdb.String()
messages    hyperdb.Multilink("msg")
files       hyperdb.Multilink("file")
nosy        hyperdb.Multilink("user")
superseder  hyperdb.Multilink("issue")
=========== ==========================

Also, two Date properties named "creation" and "activity" are
fabricated by the Roundup database layer.  By "fabricated" we
mean that no such properties are actually stored in the
hyperdatabase, but when properties on issues are requested, the
"creation" and "activity" properties are made available.
The value of the "creation" property is the date when an issue was
created, and the value of the "activity" property is the
date when any property on the issue was last edited (equivalently,
these are the dates on the first and last records in the issue's journal).

Roundupdb Interface Specification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The interface to a Roundup database delegates most method
calls to the hyperdatabase, except for the following
changes and additional methods::

    class Database:
        def getuid(self):
            """Return the id of the "user" node associated with the user
            that owns this connection to the hyperdatabase."""

    class Class:
        # Overridden methods:

        def create(self, **propvalues):
        def set(self, **propvalues):
        def retire(self, nodeid):
            """These operations trigger detectors and can be vetoed.  Attempts
            to modify the "creation" or "activity" properties cause a KeyError.
            """

        # New methods:

        def audit(self, event, detector):
        def react(self, event, detector):
            """Register a detector (see below for more details)."""

    class IssueClass(Class):
        # Overridden methods:

        def __init__(self, db, classname, **properties):
            """The newly-created class automatically includes the "messages",
            "files", "nosy", and "superseder" properties.  If the 'properties'
            dictionary attempts to specify any of these properties or a
            "creation" or "activity" property, a ValueError is raised."""

        def get(self, nodeid, propname):
        def getprops(self):
            """In addition to the actual properties on the node, these
            methods provide the "creation" and "activity" properties."""

        # New methods:

        def addmessage(self, nodeid, summary, text):
            """Add a message to an issue's mail spool.

            A new "msg" node is constructed using the current date, the
            user that owns the database connection as the author, and
            the specified summary text.  The "files" and "recipients"
            fields are left empty.  The given text is saved as the body
            of the message and the node is appended to the "messages"
            field of the specified issue.
            """

        def sendmessage(self, nodeid, msgid):
            """Send a message to the members of an issue's nosy list.

            The message is sent only to users on the nosy list who are not
            already on the "recipients" list for the message.  These users
            are then added to the message's "recipients" list.
            """


Default Schema
~~~~~~~~~~~~~~

The default schema included with Roundup turns it into a
typical software bug tracker.  The database is set up like this::

    pri = Class(db, "priority", name=hyperdb.String(), order=hyperdb.String())
    pri.setkey("name")
    pri.create(name="critical", order="1")
    pri.create(name="urgent", order="2")
    pri.create(name="bug", order="3")
    pri.create(name="feature", order="4")
    pri.create(name="wish", order="5")

    stat = Class(db, "status", name=hyperdb.String(), order=hyperdb.String())
    stat.setkey("name")
    stat.create(name="unread", order="1")
    stat.create(name="deferred", order="2")
    stat.create(name="chatting", order="3")
    stat.create(name="need-eg", order="4")
    stat.create(name="in-progress", order="5")
    stat.create(name="testing", order="6")
    stat.create(name="done-cbb", order="7")
    stat.create(name="resolved", order="8")

    Class(db, "keyword", name=hyperdb.String())

    Class(db, "issue", fixer=hyperdb.Multilink("user"),
                       topic=hyperdb.Multilink("keyword"),
                       priority=hyperdb.Link("priority"),
                       status=hyperdb.Link("status"))


(The "order" property hasn't been explained yet.  It
gets used by the Web user interface for sorting.)

The above isn't as pretty-looking as the schema specification
in the first-stage submission, but it could be made just as easy
with the addition of a convenience function like Choice
for setting up the "priority" and "status" classes::

    def Choice(name, *options):
        cl = Class(db, name, name=hyperdb.String(), order=hyperdb.String())
        for i in range(len(options)):
            cl.create(name=option[i], order=i)
        return hyperdb.Link(name)


Detector Interface
------------------

Detectors are Python functions that are triggered on certain
kinds of events.  The definitions of the
functions live in Python modules placed in a directory set aside
for this purpose.  Importing the Roundup database module also
imports all the modules in this directory, and the ``init()``
function of each module is called when a database is opened to
provide it a chance to register its detectors.

There are two kinds of detectors:

1. an auditor is triggered just before modifying an node
2. a reactor is triggered just after an node has been modified

When the Roundup database is about to perform a
``create()``, ``set()``, or ``retire()``
operation, it first calls any *auditors* that
have been registered for that operation on that class.
Any auditor may raise a *Reject* exception
to abort the operation.

If none of the auditors raises an exception, the database
proceeds to carry out the operation.  After it's done, it
then calls all of the *reactors* that have been registered
for the operation.

Detector Interface Specification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``audit()`` and ``react()`` methods
register detectors on a given class of nodes::

    class Class:
        def audit(self, event, detector):
            """Register an auditor on this class.

            'event' should be one of "create", "set", or "retire".
            'detector' should be a function accepting four arguments.
            """

        def react(self, event, detector):
            """Register a reactor on this class.

            'event' should be one of "create", "set", or "retire".
            'detector' should be a function accepting four arguments.
            """

Auditors are called with the arguments::

    audit(db, cl, nodeid, newdata)

where ``db`` is the database, ``cl`` is an
instance of Class or IssueClass within the database, and ``newdata``
is a dictionary mapping property names to values.

For a ``create()``
operation, the ``nodeid`` argument is None and newdata
contains all of the initial property values with which the node
is about to be created.

For a ``set()`` operation, newdata
contains only the names and values of properties that are about
to be changed.

For a ``retire()`` operation, newdata is None.

Reactors are called with the arguments::

    react(db, cl, nodeid, olddata)

where ``db`` is the database, ``cl`` is an
instance of Class or IssueClass within the database, and ``olddata``
is a dictionary mapping property names to values.

For a ``create()``
operation, the ``nodeid`` argument is the id of the
newly-created node and ``olddata`` is None.

For a ``set()`` operation, ``olddata``
contains the names and previous values of properties that were changed.

For a ``retire()`` operation, ``nodeid`` is the
id of the retired node and ``olddata`` is None.

Detector Example
~~~~~~~~~~~~~~~~

Here is an example of detectors written for a hypothetical
project-management application, where users can signal approval
of a project by adding themselves to an "approvals" list, and
a project proceeds when it has three approvals::

    # Permit users only to add themselves to the "approvals" list.

    def check_approvals(db, cl, id, newdata):
        if newdata.has_key("approvals"):
            if cl.get(id, "status") == db.status.lookup("approved"):
                raise Reject, "You can't modify the approvals list " \
                    "for a project that has already been approved."
            old = cl.get(id, "approvals")
            new = newdata["approvals"]
            for uid in old:
                if uid not in new and uid != db.getuid():
                    raise Reject, "You can't remove other users from the "
                        "approvals list; you can only remove yourself."
            for uid in new:
                if uid not in old and uid != db.getuid():
                    raise Reject, "You can't add other users to the approvals "
                        "list; you can only add yourself."

    # When three people have approved a project, change its
    # status from "pending" to "approved".

    def approve_project(db, cl, id, olddata):
        if olddata.has_key("approvals") and len(cl.get(id, "approvals")) == 3:
            if cl.get(id, "status") == db.status.lookup("pending"):
                cl.set(id, status=db.status.lookup("approved"))

    def init(db):
        db.project.audit("set", check_approval)
        db.project.react("set", approve_project)

Here is another example of a detector that can allow or prevent
the creation of new nodes.  In this scenario, patches for a software
project are submitted by sending in e-mail with an attached file,
and we want to ensure that there are text/plain attachments on
the message.  The maintainer of the package can then apply the
patch by setting its status to "applied"::

    # Only accept attempts to create new patches that come with patch files.

    def check_new_patch(db, cl, id, newdata):
        if not newdata["files"]:
            raise Reject, "You can't submit a new patch without " \
                          "attaching a patch file."
        for fileid in newdata["files"]:
            if db.file.get(fileid, "type") != "text/plain":
                raise Reject, "Submitted patch files must be text/plain."

    # When the status is changed from "approved" to "applied", apply the patch.

    def apply_patch(db, cl, id, olddata):
        if cl.get(id, "status") == db.status.lookup("applied") and \
            olddata["status"] == db.status.lookup("approved"):
            # ...apply the patch...

    def init(db):
        db.patch.audit("create", check_new_patch)
        db.patch.react("set", apply_patch)


Command Interface
-----------------

The command interface is a very simple and minimal interface,
intended only for quick searches and checks from the shell prompt.
(Anything more interesting can simply be written in Python using
the Roundup database module.)

Command Interface Specification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A single command, roundup, provides basic access to
the hyperdatabase from the command line::

    roundup get [-list] designator[, designator,...] propname
    roundup set designator[, designator,...] propname=value ...
    roundup find [-list] classname propname=value ...

TODO: more stuff here

Property values are represented as strings in command arguments
and in the printed results:

- Strings are, well, strings.

- Numbers are displayed the same as strings.

- Booleans are displayed as 'Yes' or 'No'.

- Date values are printed in the full date format in the local
  time zone, and accepted in the full format or any of the partial
  formats explained above.

- Link values are printed as node designators.  When given as
  an argument, node designators and key strings are both accepted.

- Multilink values are printed as lists of node designators
  joined by commas.  When given as an argument, node designators
  and key strings are both accepted; an empty string, a single node,
  or a list of nodes joined by commas is accepted.

When multiple nodes are specified to the
roundup get or roundup set
commands, the specified properties are retrieved or set
on all the listed nodes.

When multiple results are returned by the roundup get
or roundup find commands, they are printed one per
line (default) or joined by commas (with the -list) option.

Usage Example
~~~~~~~~~~~~~

To find all messages regarding in-progress issues that
contain the word "spam", for example, you could execute the
following command from the directory where the database
dumps its files::

    shell% for issue in `roundup find issue status=in-progress`; do
    > grep -l spam `roundup get $issue messages`
    > done
    msg23
    msg49
    msg50
    msg61
    shell%

Or, using the -list option, this can be written as a single command::

    shell% grep -l spam `roundup get \
        \`roundup find -list issue status=in-progress\` messages`
    msg23
    msg49
    msg50
    msg61
    shell%
    

E-mail User Interface
---------------------

The Roundup system must be assigned an e-mail address
at which to receive mail.  Messages should be piped to
the Roundup mail-handling script by the mail delivery
system (e.g. using an alias beginning with "|" for sendmail).

Message Processing
~~~~~~~~~~~~~~~~~~

Incoming messages are examined for multiple parts.
In a multipart/mixed message or part, each subpart is
extracted and examined.  In a multipart/alternative
message or part, we look for a text/plain subpart and
ignore the other parts.  The text/plain subparts are
assembled to form the textual body of the message, to
be stored in the file associated with a "msg" class node.
Any parts of other types are each stored in separate
files and given "file" class nodes that are linked to
the "msg" node.

The "summary" property on message nodes is taken from
the first non-quoting section in the message body.
The message body is divided into sections by blank lines.
Sections where the second and all subsequent lines begin
with a ">" or "|" character are considered "quoting
sections".  The first line of the first non-quoting 
section becomes the summary of the message.

All of the addresses in the To: and Cc: headers of the
incoming message are looked up among the user nodes, and
the corresponding users are placed in the "recipients"
property on the new "msg" node.  The address in the From:
header similarly determines the "author" property of the
new "msg" node.
The default handling for
addresses that don't have corresponding users is to create
new users with no passwords and a username equal to the
address.  (The web interface does not permit logins for
users with no passwords.)  If we prefer to reject mail from
outside sources, we can simply register an auditor on the
"user" class that prevents the creation of user nodes with
no passwords.

The subject line of the incoming message is examined to
determine whether the message is an attempt to create a new
issue or to discuss an existing issue.  A designator enclosed
in square brackets is sought as the first thing on the
subject line (after skipping any "Fwd:" or "Re:" prefixes).

If an issue designator (class name and id number) is found
there, the newly created "msg" node is added to the "messages"
property for that issue, and any new "file" nodes are added to
the "files" property for the issue.

If just an issue class name is found there, we attempt to
create a new issue of that class with its "messages" property
initialized to contain the new "msg" node and its "files"
property initialized to contain any new "file" nodes.

Both cases may trigger detectors (in the first case we
are calling the set() method to add the message to the
issue's spool; in the second case we are calling the
create() method to create a new node).  If an auditor
raises an exception, the original message is bounced back to
the sender with the explanatory message given in the exception.

Nosy Lists
~~~~~~~~~~

A standard detector is provided that watches for additions
to the "messages" property.  When a new message is added, the
detector sends it to all the users on the "nosy" list for the
issue that are not already on the "recipients" list of the
message.  Those users are then appended to the "recipients"
property on the message, so multiple copies of a message
are never sent to the same user.  The journal recorded by
the hyperdatabase on the "recipients" property then provides
a log of when the message was sent to whom.

Setting Properties
~~~~~~~~~~~~~~~~~~

The e-mail interface also provides a simple way to set
properties on issues.  At the end of the subject line,
``propname=value`` pairs can be
specified in square brackets, using the same conventions
as for the roundup ``set`` shell command.


Web User Interface
------------------

The web interface is provided by a CGI script that can be
run under any web server.  A simple web server can easily be
built on the standard CGIHTTPServer module, and
should also be included in the distribution for quick
out-of-the-box deployment.

The user interface is constructed from a number of template
files containing mostly HTML.  Among the HTML tags in templates
are interspersed some nonstandard tags, which we use as
placeholders to be replaced by properties and their values.

Views and View Specifiers
~~~~~~~~~~~~~~~~~~~~~~~~~

There are two main kinds of views: *index* views and *issue* views.
An index view displays a list of issues of a particular class,
optionally sorted and filtered as requested.  An issue view
presents the properties of a particular issue for editing
and displays the message spool for the issue.

A view specifier is a string that specifies
all the options needed to construct a particular view.
It goes after the URL to the Roundup CGI script or the
web server to form the complete URL to a view.  When the
result of selecting a link or submitting a form takes
the user to a new view, the Web browser should be redirected
to a canonical location containing a complete view specifier
so that the view can be bookmarked.

Displaying Properties
~~~~~~~~~~~~~~~~~~~~~

Properties appear in the user interface in three contexts:
in indices, in editors, and as filters.  For each type of
property, there are several display possibilities.  For example,
in an index view, a string property may just be printed as
a plain string, but in an editor view, that property should
be displayed in an editable field.

The display of a property is handled by functions in
a displayers module.  Each function accepts at
least three standard arguments -- the database, class name,
and node id -- and returns a chunk of HTML.

Displayer functions are triggered by <display>
tags in templates.  The call attribute of the tag
provides a Python expression for calling the displayer
function.  The three standard arguments are inserted in
front of the arguments given.  For example, the occurrence of::

    <display call="plain('status', max=30)">

in a template triggers a call to::
    
    plain(db, "issue", 13, "status", max=30)


when displaying issue 13 in the "issue" class.  The displayer
functions can accept extra arguments to further specify
details about the widgets that should be generated.  By defining new
displayer functions, the user interface can be highly customized.

Some of the standard displayer functions include:

========= ====================================================================
Function  Description
========= ====================================================================
plain     display a String property directly;
          display a Date property in a specified time zone with an option
          to omit the time from the date stamp; for a Link or Multilink
          property, display the key strings of the linked nodes (or the
          ids if the linked class has no key property)
field     display a property like the
          plain displayer above, but in a text field
          to be edited
menu      for a Link property, display
          a menu of the available choices
link      for a Link or Multilink property,
          display the names of the linked nodes, hyperlinked to the
          issue views on those nodes
count     for a Multilink property, display
          a count of the number of links in the list
reldate   display a Date property in terms
          of an interval relative to the current date (e.g. "+ 3w", "- 2d").
download  show a Link("file") or Multilink("file")
          property using links that allow you to download files
checklist for a Link or Multilink property,
          display checkboxes for the available choices to permit filtering
========= ====================================================================


Index Views
~~~~~~~~~~~

An index view contains two sections: a filter section
and an index section.
The filter section provides some widgets for selecting
which issues appear in the index.  The index section is
a table of issues.

Index View Specifiers
"""""""""""""""""""""

An index view specifier looks like this (whitespace
has been added for clarity)::

    /issue?status=unread,in-progress,resolved&amp;
        topic=security,ui&amp;
        :group=+priority&amp;
        :sort=-activity&amp;
        :filters=status,topic&amp;
        :columns=title,status,fixer


The index view is determined by two parts of the
specifier: the layout part and the filter part.
The layout part consists of the query parameters that
begin with colons, and it determines the way that the
properties of selected nodes are displayed.
The filter part consists of all the other query parameters,
and it determines the criteria by which nodes 
are selected for display.

The filter part is interactively manipulated with
the form widgets displayed in the filter section.  The
layout part is interactively manipulated by clicking
on the column headings in the table.

The filter part selects the union of the
sets of issues with values matching any specified Link
properties and the intersection of the sets
of issues with values matching any specified Multilink
properties.

The example specifies an index of "issue" nodes.
Only issues with a "status" of either
"unread" or "in-progres" or "resolved" are displayed,
and only issues with "topic" values including both
"security" and "ui" are displayed.  The issues
are grouped by priority, arranged in ascending order;
and within groups, sorted by activity, arranged in
descending order.  The filter section shows filters
for the "status" and "topic" properties, and the
table includes columns for the "title", "status", and
"fixer" properties.

Associated with each issue class is a default
layout specifier.  The layout specifier in the above
example is the default layout to be provided with
the default bug-tracker schema described above in
section 4.4.

Filter Section
""""""""""""""

The template for a filter section provides the
filtering widgets at the top of the index view.
Fragments enclosed in ``<property>...</property>``
tags are included or omitted depending on whether the
view specifier requests a filter for a particular property.

Here's a simple example of a filter template::

    <property name=status>
        <display call="checklist('status')">
    </property>
    <br>
    <property name=priority>
        <display call="checklist('priority')">
    </property>
    <br>
    <property name=fixer>
        <display call="menu('fixer')">
    </property>

Index Section
"""""""""""""

The template for an index section describes one row of
the index table.
Fragments enclosed in ``<property>...</property>``
tags are included or omitted depending on whether the
view specifier requests a column for a particular property.
The table cells should contain <display> tags
to display the values of the issue's properties.

Here's a simple example of an index template::

    <tr>
        <property name=title>
            <td><display call="plain('title', max=50)"></td>
        </property>
        <property name=status>
            <td><display call="plain('status')"></td>
        </property>
        <property name=fixer>
            <td><display call="plain('fixer')"></td>
        </property>
    </tr>

Sorting
""""""""""""""

String and Date values are sorted in the natural way.
Link properties are sorted according to the value of the
"order" property on the linked nodes if it is present; or
otherwise on the key string of the linked nodes; or
finally on the node ids.  Multilink properties are
sorted according to how many links are present.

Issue Views
~~~~~~~~~~~

An issue view contains an editor section and a spool section.
At the top of an issue view, links to superseding and superseded
issues are always displayed.

Issue View Specifiers
"""""""""""""""""""""

An issue view specifier is simply the issue's designator::

    /patch23


Editor Section
""""""""""""""

The editor section is generated from a template
containing <display> tags to insert
the appropriate widgets for editing properties.

Here's an example of a basic editor template::

    <table>
    <tr>
        <td colspan=2>
            <display call="field('title', size=60)">
        </td>
    </tr>
    <tr>
        <td>
            <display call="field('fixer', size=30)">
        </td>
        <td>
            <display call="menu('status')>
        </td>
    </tr>
    <tr>
        <td>
            <display call="field('nosy', size=30)">
        </td>
        <td>
            <display call="menu('priority')>
        </td>
    </tr>
    <tr>
        <td colspan=2>
            <display call="note()">
        </td>
    </tr>
    </table>

As shown in the example, the editor template can also
request the display of a "note" field, which is a
text area for entering a note to go along with a change.

When a change is submitted, the system automatically
generates a message describing the changed properties.
The message displays all of the property values on the
issue and indicates which ones have changed.
An example of such a message might be this::

    title: Polly Parrot is dead
    priority: critical
    status: unread -> in-progress
    fixer: (none)
    keywords: parrot,plumage,perch,nailed,dead

If a note is given in the "note" field, the note is
appended to the description.  The message is then added
to the issue's message spool (thus triggering the standard
detector to react by sending out this message to the nosy list).

Spool Section
"""""""""""""

The spool section lists messages in the issue's "messages"
property.  The index of messages displays the "date", "author",
and "summary" properties on the message nodes, and selecting a
message takes you to its content.


Deployment Scenarios
--------------------

The design described above should be general enough
to permit the use of Roundup for bug tracking, managing
projects, managing patches, or holding discussions.  By
using nodes of multiple types, one could deploy a system
that maintains requirement specifications, catalogs bugs,
and manages submitted patches, where patches could be
linked to the bugs and requirements they address.


Acknowledgements
----------------

My thanks are due to Christy Heyl for 
reviewing and contributing suggestions to this paper
and motivating me to get it done, and to
Jesse Vincent, Mark Miller, Christopher Simons,
Jeff Dunmall, Wayne Gramlich, and Dean Tribble for
their assistance with the first-round submission.

Changes to this document
------------------------

- Added Boolean and Number types
- Added section Hyperdatabase Implementations
- "Item" has been renamed to "Issue" to account for the more specific nature
  of the Class.