OpenACS Packages

By Pete Su and Bryan Quinn

OpenACS docs are written by the named authors, and may be edited by OpenACS documentation staff.


This document is a guide on how to write a software package for OpenACS. OpenACS packages are installed and maintained with the OpenACS Package Manager (APM) which is part of the acs-admin package. This document presents reasons for packaging software, conventions for the file system and naming that must be followed, and step by step instructions for creating a new package for the "Notes" example package.

Server file layout

Here is how an OpenACS 5 server is laid out starting from the Server root (ROOT):

Figure 11.1. Server file layout diagram

        Various executables and scripts for server maintenance.
        content repository content stored in the filesystem.
        Installation scripts and configuration files.
        ... many many more...
        Server error and access logs
        bootstrap code
        Pages not in packages (static content, customized pages)

What a Package Looks Like

Each package encapsulates all of its data model, library code, logic, administration pages and user pages in a single part of the file tree. This means developers can track down everything that is related to a particular package without hunting all over the file system. Encapsulating everything about a package in one place also makes it much easier to distribute packages independently from the OpenACS Core.

In order to make this work, we need a system that keeps track of the packages that have been installed in the server, where those packages have been installed, and a standard way to map URLs that a client sends to our server to the right page in the appropriate package. While we're at it, this tool should also automate package installation, dependency checking, upgrades, and package removal. In OpenACS 5, this tool is called the APM.

To illustrate the general structure of a package, let's see what the package for the "notes" application should look like.

Figure 11.2. Package file layout diagram

  +-- packages/    APM Root
        +-- notes/  Package Root 
        |     |
        |     +--                              Package Specification File
        |     +-- sql/
        |     |     |
        |     |     +-- oracle/
        |     |     |        |
        |     |     |        +-- notes-create.sql         Data Model Creation Script for Oracle
        |     |     |        +-- notes-drop.sql           Data Model Drop Script
        |     |     |        +-- *.sql                    Data Model Files
        |     |     |        +-- upgrade/
        |     |     |            +-- upgrade-4.1-4.5.sql  Data Model Upgrade Scripts
        |     |     +-- postgresql/
        |     |     |        |
        |     |     |        +-- notes-create.sql         Data Model Creation Script for PostgreSQL      
        |     |     |        +-- notes-drop.sql           Data Model Drop Script
        |     |     |        +-- *.sql                    Data Model Files
        |     |     |        +-- upgrade/
        |     |     |            +-- upgrade-4.1-4.5.sql  Data Model Upgrade Scripts
        |     +-- tcl/
        |     |     |
        |     |     +-- notes-procs.tcl                   Tcl Library
        |     |     +-- notes-procs.xql                   SQL92 Queries for notes-procs.tcl
        |     |     +-- notes-procs-oracle.xql            Oracle-specific queries for notes-procs.tcl
        |     |     +-- notes-procs-postgresql.xql        PostgreSQL-specific Queries for notes-procs.tcl
        |     |     +-- notes-init.tcl                    Tcl Initialization
        |     |     +-- notes-init.xql                    Queries for notes-init.tcl (work in all DBs)      
        |     |     +-- *.tcl                             Tcl Library Files
        |     +-- lib/
        |     |     |
        |     |     +-- *.tcl                             Includable page logic
        |     |     +-- *.adp                             Includable page templates
        |     +-- www/
        |     |     |
        |     |     +-- admin/                            Administration UI
        |     |     |     +-- tests/                      Regression Tests
        |     |     |     |     +-- index.tcl             Regression Test Index Page
        |     |     |     |     +-- ...                   Regression Tests
        |     |     |     +-- index.tcl                   Administration UI Index Page
        |     |     |     +-- ...                         Administration UI Pages
        |     |     |
        |     |     +-- doc/                              Documentation
        |     |     |     +-- index.html                  Documentation Index Page
        |     |     |     +-- ...                         Administration Pages
        |     |     +-- resources/                        Static Content
        |     |     |     +-- ...                         Static Content files
        |     |     +-- index.tcl                         UI Index Page
        |     |     +-- index.adp                         UI Index Template
        |     |     +-- index.xql                         Queries for UI Index page      
        |     |     +-- *.tcl                             UI Logic Scripts
        |     |     +-- *.adp                             UI Templates
        |     |     +-- *-oracle.xql                      Oracle-specific Queries
        |     |     +-- *-postgresql.xql                  PostgreSQL-specific Queries
        +-- Other package directories.

All file locations are relative to the package root, which in this case is ROOT/packages/notes. The following table describes in detail what each of the files up in the diagram contain.

A special note on the PACKAGE-KEY/www/resources directory. Files in this directory are available at http://yourserver/resources/PACKAGE-KEY/... and are returned without any permissions checking or even checks that the package is installed or mounted. Files are returned directly, so .tcl or .adp files are not sourced in these directories. This makes it suitable for storing icons, css files, javascript, and other static content which can be treated this way.

Table 11.1. Package files

File TypeIts UseNaming Convention
Package Specification FileThe package specification file is an XML file generated and maintained by the OpenACS Package Manager (APM). It specifies information about the package including its parameters and its
Data Model Creation ScriptContains the SQL that creates the necessary data model and PL/SQL packages (or PL/pgSQL or whatever) to support the package. The name must match the convention below or the package will not be installed correctly. Notice that the script must be under the appropriate directory for the database you are developing your package for (hopefully all OpenACS-supported databases :-))sql/<database>/notes-create.sql
Data Model Drop ScriptContains the SQL that removes the data model and PL/SQL packages generated by the creation script. The name must match the convention below or the package will not be installed correctly.sql/<database>/notes-drop.sql
Data Model FileAny .sql file that does not match the naming convention above is recognized as a data model file. It is useful to separate the SQL in the creation and drop scripts into several files and then have the scripts source the other data model files. In Oracle this can be done by including @@ filename in the creation or drop scripts. See the Oracle FAQ for examples. In PostgreSQL the same is accomplished by including \i filename.sql/<database>/*.sql
Data Model Upgrade ScriptsContain changes to the data model between versions. The APM can automatically load the appropriate upgrade scripts when upgrading to a new version of a package.sql/<database>/upgrade/upgrade-<old>-<new>.sql
SQL92 Query FilesFiles with queries that are supported by all databases. These are usually SQL92 queries. Notice that the .xql filename must match the name of the .tcl file that uses those queries.*.xql
Oracle-specific Query FilesFiles with queries that are Oracle-specific. Notice that the .xql filename must match the name of the .tcl file that uses those queries.*-oracle.xql
PostgreSQL-specific Query FilesFiles with queries that are PostgreSQL-specific. Notice that the .xql filename must match the name of the .tcl file that uses those queries.*-postgresql.xql
Tcl Library FilesThe Tcl library files include a set of procedures that provide an application programming interface (API) for the package to utilize.tcl/notes-procs.tcl
Tcl InitializationThe initialization files are used to run Tcl procedures that should only be sourced once on startup. Examples of statements to put here are registered filters or procedures. Tcl initialization files are sourced once on server startup after all of the Tcl library files are sourced.tcl/notes-init.tcl
Administration UIThe administration UI is used to administer the instances of the package. For example, the forums administration UI is used to create new forums, moderate postings, and create new categories for forums postings.www/admin/*
Administration UI Index PageEvery package administration UI must have an index page. In most cases, this is index.tcl but it can be any file with the name index, such as index.html or index.adp.www/admin/index.tcl
Regression TestsEvery package should have a set of regression tests that verify that it is in working operation. These tests should be able to be run at any time after the package has been installed and report helpful error messages when there is a fault in the system.www/admin/tests/
Regression Test Index PageThe regression test directory must have an index page that displays all of the tests available and provides information on how to run them. This file can have any extension, as long as its name is index.www/admin/tests/index.html
DocumentationEvery package must include a full set of documentation that includes requirements and design documents, and user-level and developer-level documentation where appropriate.www/doc/
Documentation Index PageThe documentation directory must include a static HTML file with the name of index.html.www/doc/index.html
UI Logic ScriptsPackages provide a UI for users to access the system. The UI is split into Logic and Templates. The logic scripts perform database queries and prepare variables for presentation by the associated templates.www/*.tcl
UI TemplatesTemplates are used to control the presentation of the UI. Templates receive a set of data sources from the logic scripts and prepare them for display to the browser.www/*.adp
UI Index PageThe UI must have an index page composed of a logic script called index.tcl and a template called index.adp.www/index.tcl


The APM is used to create, maintain, and install packages. It takes care of copying all of the files and registering the package in the system. The APM is responsible for:

  1. Package registration

  2. Automatic installation of packages: loading data models, code libraries, and so on.

  3. Checking what packages depend on what other packages.

  4. Storing information on the package including ownership and a file list.

In addition for packages that are applications, the APM is responsible for keeping track of where in the site a user must go in order to use the application. To do this, the APM defines a set of objects that we call package instances. Once a package is loaded, the administrator can create as many instances of the package as she likes, and map these instances to any URL in the site that she wants. If packages are analogous to executable programs in an operating system, then package instances are analgous to multiple running copies of a single program. Each instance can be independently administered and each instance maintains its own set of application parameters and options.

The following sections will show you how to make a package for the Notes application. In addition, they will discuss some site management features in OpenACS 5 that take advantage of the APM's package instance model. The two most important of these are subsites, and the site map tool, which can be used to map applications to one or more arbitrary URLs in a running site.

We will also discuss how to organize your files and queries so they work with the OpenACS Query Dispatcher.

Making a Package

Here is how you make a package.

  1. Login as a site-wide administrator on your web service.

  2. Go to the package manager on your server. The URL is /acs-admin/apm.

  3. Click on the link /acs-admin/apm/package-add.

  4. Fill out the form for adding a new package. The form explains what everything means, but we'll repeat the important bits here for easy reference:

    Package Key

    This is a short text string that should uniquely name your package to distinguish it from all the others. It is used as a database key to keep track of the package and as the name of the directory in the file system where all the files related to your package will live. Example package keys in the current system include: forums, acs-kernel and so on. For the example application, we will use the package key notes.

    Package Name

    This is a short human readable name for your package. For our example, we will use the name "Notes".

    Package Plural

    If your package name is a nice singular noun, this should be the plural form of it. I assume the plural form is used when multiple instances of the package are used by a single service. We'll talk more about package instances later. Our example application doesn't really have a good plural name. So just make it also be "Notes".

    Package Type

    Generally we think of packages as either being applications, meaning that the package is meant primarily for use by end-users, or services meaning that the package is meant to be a reusable library of code, to be used by other packages. forums is a good example of an application, while acs-templating is a good example of a service. Our example is an application, so pick that.

    Package URL

    The URL from which people will download your package when it is done. Just use the default for this, you can change it later.

    Initial Version

    Just use the default here, which by convention is 0.1d.

    Version URL

    Just use the default here.

    Summary and Description

    Enter a short summary and longer description of what the Notes application will do. That is, something like "this application keeps short textual notes in the database", and so on.

  5. Click the button "Create Package".

  6. At this point, APM will create a directory called ROOT/packages/notes.

  7. The directory that APM created will be empty except for the file. Create a file called ROOT/packages/notes/sql/oracle/notes-create.sql. We'll fill this file with our data model very soon. Create a file called ROOT/packages/notes/sql/oracle/notes-drop.sql. This will contain the instructions to drop the data model. To be complete, you would also create the PostgreSQL versions of these files as well in ROOT/packages/notes/sql/postgresql/notes-create.sql and ROOT/packages/notes/sql/postgresql/notes-drop.sql.

    After you do this, go back to the main APM page. From there, click the link called "notes" to go to the management page for the new package. Now click the link called "Manage file information", then the "Scan the packages/notes directory for additional files in this package" link on that page to scan the file system for new files. This will bring you do a page that lists all the files you just added and lets you add them to the notes package.

    Note that while the .sql files have been added to the package, they have not been loaded into the database. For the purposes of development, you have to load the data model by hand, because while OpenACS has automatic mechanisms for loading and reloading .tcl files for code, it does not do the same thing for data model files.

  8. Now go back to the main management page for the notes If your package has parameters, create them using the "Manage Parameter Information" link. Define package callbacks via the "Tcl Callbacks (install, instantiate, mount)" link.

  9. The new package has been created and installed in the server. At this point, you should add your package files to your CVS repository. I'll assume that you have set up your development repository according to the standards described in this appendix. If so, then you just do this:

    % cd ROOT/packages
    % cvs add notes
    % cd notes
    % cvs add
    % cvs add sql
    % cd sql
    % cvs add *.sql
    % cd ROOT/packages/notes
    % cvs commit -m "add new package for notes"
  10. Now you can start developing the package. In addition to writing code, you should also consider the tasks outlined in the package development tutorial.

The Site Map and Package Instances

At this point, you are probably excited to see your new package in action. But, we haven't added any user visible pages yet. By convention, user visible pages go in the ROOT/packages/notes/www directory. So go there and add a file called hello.html with some text in it. Now we have to make the user pages visible in the site. Since we didn't put the pages underneath ROOT/www they will not appear on their own. What we have to do is mount the application into the site map. That is, we have to define the URL from which the application will serve its pages.

In OpenACS 5, administrators can define an arbitrary mapping between the URLs the user types and the actual file in the file system that is served. This mapping is called the site map and entries in the site map are called site nodes. Each site node maps a URL to an OpenACS object. Since package instances are objects, the site map allows us to easily map package instances to URLs. As we said before, each instance of an application has its own set of parameters and runs from its own URL within the site. What this means is that even though all the code for the notes application lives in ROOT/packages/notes, the application itself can run from any number of locations in the site. This allows developers and administrators to build sites that look to the user like a collection of many independent applications that actually run on a single shared code base. The request-processor document shows you how OpenACS figures out which instance of your application was requested by the user at any given time. The page development tutorial shows you how to use this information in your user interface.

In order to make the new notes application visible to users, we have to mount it in the site map. You do this by going to the Site Map page, which is by default available at /acs-admin/site-map. Use the interface here to add a new sub-folder called notes to the root of the site, then click "new application" to mount a new instance of the notes application to the site. Name the new instance notes-1.

Then type this URL into your browser: http://yourserver/notes/hello.html

Now you should see the contents of the page that you added. What has happened is that all URLs that start with /notes have been mapped in such a way as to serve content from the directory ROOT/packages/notes/www. At this point, you can experiment with the site map by mounting multiple instances of the not yet written Notes application at various places in the site. In a later document, we'll see how to write your application so that the code can detect from what URL it was invoked. This is the key to supporting subsites.


The APM performs the following tasks in an OpenACS site:

  • Manages creation, installation, and removal of packages from the server. Also keeps track of what files belong to which packages.

  • Manages package upgrades.

  • Manages information on all package instances in a site. For correctly written application packages, this allows the site administrator to map multiple instances of a package to URLs within a site.

  • Writes out package distribution files for other people to download and install. We'll cover this later.

Additional Reading

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