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<sect1 id="subsites-design" xreflabel="OpenACS 4 Subsites Design Document">
<title>Subsites Design Document</title>
<authorblurb>
<para>By <ulink url="http://planitia.org">Rafael H. Schloming</ulink> </para>
</authorblurb>
<para><emphasis>*Note* This document has not gone through the any of the
required QA process yet. It is being tagged as stable due to high
demand.</emphasis></para>
<sect2 id="subsites-design-essentials">
<title>Essentials</title>
<itemizedlist>
<listitem>
<para><xref linkend="subsites-requirements"/></para>
</listitem>
</itemizedlist>
</sect2>
<sect2 id="subsites-design-intro">
<title>Introduction</title>
<para>An OpenACS 4 subsite is a managed suite of applications that work together for
a particular user community. This definition covers a very broad range of
requirements: from a Geocities style homepage where a user can install
whatever available application he wants (e.g. a single user could have their
own news and forums), to a highly structured project subsite with multiple
interdependent applications. Thus, flexibility in application deployment is
the overarching philosophy of subsites.</para>
<para>Meeting such broad requirements of flexibility demands architecture-level
support, i.e. very low-level support from the core OpenACS 4 data model. For
example, the subsites concept demands that any package can have multiple
instances installed at different URLs - entailing support from the APM and
the Request Processor. Since the design and implementation directly
associated with subsites is actually minimal, a discussion of subsites design
is, in fact, a discussion of how core OpenACS 4 components implicitly support
subsites as a whole.</para>
</sect2>
<sect2 id="subsites-design-hist-considerations">
<title>Historical Considerations</title>
<para>The subsites problem actually has several quite diverse origins. It was
originally recognized as a toolkit feature in the form of
"scoping". The basic concept behind scoping was to allow one scoped
OpenACS installation to behave as multiple unscoped OpenACS installations so that one
OpenACS install could serve multiple communities. Each piece of application data
was tagged with a "scope" consisting of the (user_id, group_id,
scope) triple. In practice the highly denormalized data models that this
method uses produced large amounts of very redundant code and in general made
it an extremely cumbersome process to "scopify" a module.</para>
<para>Before the advent of scoping there were several cases of client projects
implementing their own version of scoping in special cases. One example being
the wineaccess multi-retailer ecommerce. (Remember the other examples and get
details. Archnet?, iluvcamp?)</para>
<para>The requirements of all these different projects vary greatly, but the one
consistent theme among all of them is the concept that various areas of the
web site have their own private version of a module. Because this theme is so
dominant, this is the primary problem that the OpenACS4 implementation of
subsites addresses.</para>
</sect2>
<sect2 id="subsites-design-competitors">
<title>Competitive Analysis</title>
<para>...</para>
</sect2>
<sect2 id="subsites-design-design-tradeoffs">
<title>Design Tradeoffs</title>
<para>The current implementation of package instances and subsites allows
extremely flexible URL configurations. This has the benefit of allowing
multiple instances of the same package to be installed in one subsite, but
can potentially complicate the process of integrating packages with each
other since it is likely people will want packages that live at non standard
URLs to operate together. This requirement would cause some packages to have
more configuration options than normal since hard-coding the URLs would not
be feasible anymore.</para>
</sect2>
<sect2 id="subsites-design-api">
<title>API</title>
<para>This section will cover all the APIs relevant to subsites, and so will
consist of portions of the APIs of several systems.</para>
<para><emphasis role="strong">Packages</emphasis></para>
<para>The following package is provided for instantiation of packages. The
apm_package.new function can be used to create a package of any type known to
the system. The apm_package_types table can be queried for a list of
installed packages. (See APM docs for more detail XXX: insert link here)</para>
<programlisting>
<computeroutput>create or replace package apm_package
as
function new (
package_id in apm_packages.package_id%TYPE
default null,
instance_name in apm_packages.instance_name%TYPE
default null,
package_key in apm_packages.package_key%TYPE,
object_type in acs_objects.object_type%TYPE
default 'apm_package',
creation_date in acs_objects.creation_date%TYPE
default sysdate,
creation_user in acs_objects.creation_user%TYPE
default null,
creation_ip in acs_objects.creation_ip%TYPE
default null,
context_id in acs_objects.context_id%TYPE
default null
) return apm_packages.package_id%TYPE;
procedure delete (
package_id in apm_packages.package_id%TYPE
);
function singleton_p (
package_key in apm_packages.package_key%TYPE
) return integer;
function num_instances (
package_key in apm_package_types.package_key%TYPE
) return integer;
function name (
package_id in apm_packages.package_id%TYPE
) return varchar;
-- Enable a package to be utilized by a subsite.
procedure enable (
package_id in apm_packages.package_id%TYPE
);
procedure disable (
package_id in apm_packages.package_id%TYPE
);
function highest_version (
package_key in apm_package_types.package_key%TYPE
) return apm_package_versions.version_id%TYPE;
end apm_package;
/
show errors
</computeroutput>
</programlisting>
<para><emphasis role="strong">Site Nodes</emphasis></para>
<para>This data model keeps track of what packages are being served from what
URLs. You can think of this as a kind of rp_register_directory_map on drugs.
This table represents a fully hierarchical site map. The directory_p column
indicates whether or not the node is a leaf node. The pattern_p column
indicates whether an exact match between the request URL and the URL of the
node is required. If pattern_p is true then a match between a request URL and
a site node occurs if any valid prefix of the request URL matches the site
node URL. The object_id column contains the object mounted on the URL
represented by the node. In most cases this will be a package instance.</para>
<programlisting>
<computeroutput>create table site_nodes (
node_id constraint site_nodes_node_id_fk
references acs_objects (object_id)
constraint site_nodes_node_id_pk
primary key,
parent_id constraint site_nodes_parent_id_fk
references site_nodes (node_id),
name varchar(100)
constraint site_nodes_name_ck
check (name not like '%/%'),
constraint site_nodes_un
unique (parent_id, name),
-- Is it legal to create a child node?
directory_p char(1) not null
constraint site_nodes_directory_p_ck
check (directory_p in ('t', 'f')),
-- Should URLs that are logical children of this node be
-- mapped to this node?
pattern_p char(1) default 'f' not null
constraint site_nodes_pattern_p_ck
check (pattern_p in ('t', 'f')),
object_id constraint site_nodes_object_id_fk
references acs_objects (object_id)
);
</computeroutput>
</programlisting>
<para>The following package is provided for creating nodes.</para>
<programlisting>
<computeroutput>create or replace package site_node
as
-- Create a new site node. If you set directory_p to be 'f' then you
-- cannot create nodes that have this node as their parent.
function new (
node_id in site_nodes.node_id%TYPE default null,
parent_id in site_nodes.node_id%TYPE default null,
name in site_nodes.name%TYPE,
object_id in site_nodes.object_id%TYPE default null,
directory_p in site_nodes.directory_p%TYPE,
pattern_p in site_nodes.pattern_p%TYPE default 'f'
) return site_nodes.node_id%TYPE;
-- Delete a site node.
procedure delete (
node_id in site_nodes.node_id%TYPE
);
-- Return the node_id of a URL. If the url begins with '/' then the
-- parent_id must be null. This will raise the no_data_found
-- exception if there is no matching node in the site_nodes table.
-- This will match directories even if no trailing slash is included
-- in the url.
function node_id (
url in varchar,
parent_id in site_nodes.node_id%TYPE default null
) return site_nodes.node_id%TYPE;
-- Return the url of a node_id.
function url (
node_id in site_nodes.node_id%TYPE
) return varchar;
end;
/
show errors
</computeroutput>
</programlisting>
<para><emphasis role="strong">Request Processor</emphasis></para>
<para>Once the above APIs are used to create packages and mount them on a
specific site node, the following request processor APIs can be used to allow
the package to serve content appropriate to the package instance.</para>
<programlisting>
<computeroutput>[ad_conn node_id]
[ad_conn package_id]
[ad_conn package_url]
[ad_conn subsite_id]
[ad_conn subsite_url]
</computeroutput>
</programlisting>
</sect2>
<sect2 id="subsites-design-data-model">
<title>Data Model Discussion</title>
<para>The subsites implementation doesn't really have it's own data
model, although it depends heavily on the site-nodes data model, and the APM
data model.</para>
</sect2>
<sect2 id="subsites-design-ui">
<title>User Interface</title>
<para>The primary elements of the subsite user interface consist of the subsite
admin pages. These pages are divided up into two areas: Group administration,
and the site map. The group administration pages allow a subsite
administrator to create and modify groups. The site map pages allow a subsite
administrator to install, remove, configure, and control access to packages.
The site map interface is the primary point of entry for most of the things a
subsite administrator would want to do.</para>
</sect2>
<sect2 id="subsites-design-config">
<title>Configuration/Parameters</title>
<para>...</para>
</sect2>
<sect2 id="subsites-design-future">
<title>Future Improvements/Areas of Likely Change</title>
<para>The current subsites implementation addresses the most basic functionality
required for subsites. It is likely that as developers begin to use the
subsites system for more sophisticated projects, it will become necessary to
develop tools to help build tightly integrated packages. The general area
this falls under is "inter-package communication". An actual
implementation of this could be anything from clever use of configuration
parameters to lots of package level introspection. Another area that is
currently underdeveloped is the ability to "tar up" and distribute
a particular configuration of site nodes/packages. As we build more
fundamental applications that can be applied in more general areas, this
feature will become more and more in demand since more problems will be
solvable by configuration instead of coding.</para>
</sect2>
<sect2 id="subsites-design-authors">
<title>Authors</title>
<para><ulink url="mailto:rhs@mit.edu">rhs@mit.edu</ulink></para>
</sect2>
</sect1>
