In general terms, a package is a unit of software that serves a single well-defined purpose. That purpose may be to provide a service directly to one or more classes of end-user, (e.g., discussion forums and file storage for community members, user profiling tools for the site publisher), or it may be to act as a building block for other packages (e.g., an application programming interface (API) for storing and querying access control rules, or an API for scheduling email alerts). Thus, packages fall into one of two categories:

An installation of the OpenACS includes the OpenACS Kernel, some services that extend the kernel's functionality, and some applications intended for end-users. Packages function as individual pieces of subsites. A subsite can contain multiple application and service instances that provide the end-user with capabilities and content customized to the particular subsite.

This architecture supports the growth of collaborative commerce. For example, Jane User starts a forum focusing on the merits of View Cameras by creating an instance of the Forum application for her personal subsite on an OpenACS Installation. Jack User discovers Jane's forum and includes a link to it in his subsite. As interest in Jane's forum grows, she creates a subsite specializing in providing information about View cameras. This subsite now includes several package instances beyond Forum; it could potentially include its own Ecommerce capabilities (ala Yahoo! Shopping). This could include a knowledge management application that allows users to spread expertise about view cameras and a portal application that links to reliable camera models and resellers. Any subsite enabled package that is added to the OpenACS installation through APM is another potential package instance that can become part of Jane's View Camera subsite.

The APM provides an architecture for packaging software, making instances of that software available to subsites, specifying configuration parameters for each instance, and managing the creation and release of new packages.

Prior to ACS 3.3, all packages were lumped together into one monolithic distribution without explicit boundaries; the only way to ascertain what comprised a given package was to look at the top of the corresponding documentation page, where, by convention, the package developer would specify where to find:

Experience has shown us that this lack of explicit boundaries causes a number of maintainability problems for pre-3.3 installations:

Consistent use of the APM format and tools will go a long way toward solving the maintainability problems listed above. Moreover, APM is the substrate that will enable us to soon establish a central package repository, where both ArsDigita and third-party developers will be able publish their packages for other ACS users to download and install.

For a simple illustration of the difference between ACS without APM (pre-3.3) and ACS with APM (3.3 and beyond), consider a hypothetical ACS installation that uses only two of the thirty-odd modules available circa ACS 3.2 (say, bboard and e-commerce):

[D]

APM itself is part of a package, the OpenACS Kernel, an OpenACS service that is the only mandatory component of an OpenACS installation.

The OpenACS is a platform for web-based application software, and any software platform has the potential to develop problems like those described above. Fortunately, there are many precedents for systematic solutions, including:

Borrowing from all of the above, OpenACS 3.3 introduces its own package management system, the OpenACS Package Manager (APM), which consists of:

The design chosen for APM was meant to satisfy the following constraints:

All of these requirements were met, but at the cost of development simplicity. As Packages demonstrates, a set of strict directory conventions are required in order for a package to use APM. This contrasts with the apparent simplicity available to developers of the OpenACS 3.3 system. However, while the system has become more complex for developers to build packages, this complexity is easily managed and is compensated for by additional capabilities.

For example, to make a new application available to the system, a developer must:

While this is complex, especially to a new OpenACS developer, the documentation walks the developer through each of these steps. Moreover, from following these steps, the package can be subsite specific, available to subsites across the system, and be available for distribution to other OpenACS installations without doing a monolithic upgrade or reinstall.

The APM is composed of systems for accomplishing a set of package-related tasks. Each of these tasks comprise a feature area that has an API, data model, and a UI:

Authoring a Package

Full instructions on how to prepare an OpenACS package are available in Packages. The API here can be invoked manually by a package's data model creation script, but need not to be used. This API is part of the APM PL/SQL package.

-- Informs the APM that this application is available for use.
procedure register_application (
    package_key         in apm_package_types.package_key%TYPE,
    pretty_name         in apm_package_types.pretty_name%TYPE,
    pretty_plural       in apm_package_types.pretty_plural%TYPE,
    package_uri         in apm_package_types.package_uri%TYPE,
    singleton_p         in apm_package_types.singleton_p%TYPE
                                default 'f',
    spec_file_path      in apm_package_types.spec_file_path%TYPE
                                default null,
    spec_file_mtime     in apm_package_types.spec_file_mtime%TYPE
                                default null
);

The procedure above registers an OpenACS application in the APM. It creates a new OpenACS object and stores information about the package, such as its name, in the APM data model. There is an analogous procedure for OpenACS services, called apm.register_service.

To remove an application from the system, there are the calls apm.unregister_application and apm.unregister_service.

-- Remove the application from the system.  
procedure unregister_application (
    package_key     in apm_package_types.package_key%TYPE,
    -- Delete all objects associated with this application.
    cascade_p       in char default 'f'  
);

Use the cascade_p only if you want to completely remove the package from the OpenACS.

In order to determine if a particular package exists in the system, use the register_p predicate. It returns 1 if the specified package_key exists in the system, 0 otherwise.

function register_p (
    package_key     in apm_package_types.package_key%TYPE
) return integer;

Maintaining Multiple Versions of a Package

While the package authoring API provides a means for registering a package, some information about a package is version dependent. For example, between versions, the owner of a package, its vendor, its URI, and its dependency information may change. The API for package versions allows this information to be specified. All of these APIs are part of the apm_package_version PL/SQL package.

To create a new package version, use the apm_package_version.new constructor function.

function new (
    version_id          in apm_package_versions.version_id%TYPE
                default null,
    package_key         in apm_package_versions.package_key%TYPE,
    version_name        in apm_package_versions.version_name%TYPE
                                default null,
    version_uri         in apm_package_versions.version_uri%TYPE,
    summary         in apm_package_versions.summary%TYPE,
    description_format      in apm_package_versions.description_format%TYPE,
    description         in apm_package_versions.description%TYPE,
    release_date        in apm_package_versions.release_date%TYPE,
    vendor          in apm_package_versions.vendor%TYPE,
    vendor_uri          in apm_package_versions.vendor_uri%TYPE,
    installed_p         in apm_package_versions.installed_p%TYPE
                                default 'f',
    data_model_loaded_p     in apm_package_versions.data_model_loaded_p%TYPE
                        default 'f'
) return apm_package_versions.version_id%TYPE;

In order to use this function, an existing package_key must be specified. The version_name parameter must follow a strict convention:

In addition, the letters d, a, and b may be followed by another integer, indicating a version within the release.

For those who like regular expressions:

version_number := ^[0-9]+((\.[0-9]+)+((d|a|b|)[0-9]?)?)$

So the following is a valid progression for version numbers:

To delete a given version of a package, use the apm_package_version.delete procedure:

procedure delete (
    package_id      in apm_packages.package_id%TYPE  
);

After creating a version, it is possible to edit the information associated with it using apm_package_version.edit.

function edit (
      new_version_id        in apm_package_versions.version_id%TYPE
                default null,
      version_id        in apm_package_versions.version_id%TYPE,
      version_name      in apm_package_versions.version_name%TYPE
                default null,
      version_uri       in apm_package_versions.version_uri%TYPE,
      summary           in apm_package_versions.summary%TYPE,
      description_format    in apm_package_versions.description_format%TYPE,
      description       in apm_package_versions.description%TYPE,
      release_date      in apm_package_versions.release_date%TYPE,
      vendor            in apm_package_versions.vendor%TYPE,
      vendor_uri        in apm_package_versions.vendor_uri%TYPE,
      installed_p       in apm_package_versions.installed_p%TYPE
                default 'f',
      data_model_loaded_p   in apm_package_versions.data_model_loaded_p%TYPE
                default 'f'
) return apm_package_versions.version_id%TYPE;

Versions can be enabled or disabled. Enabling a version instructs APM to source the package's libraries on startup and to make the package available to the OpenACS.

procedure enable (
    version_id          in apm_package_versions.version_id%TYPE
);

procedure disable (
    version_id          in apm_package_versions.version_id%TYPE  
);

Files associated with a version can be added and removed. The path is relative to the package-root which is acs-server-root/packages/package-key.

-- Add a file to the indicated version. 
function add_file(
    file_id             in apm_package_files.file_id%TYPE 
                        default null, 
    version_id in       apm_package_versions.version_id%TYPE, 
    path                in apm_package_files.path%TYPE,
    file_type           in apm_package_file_types.file_type_key%TYPE 
) return apm_package_files.file_id%TYPE; 

-- Remove a file from the indicated version.
procedure remove_file( 
    version_id          in apm_package_versions.version_id%TYPE,
    path                in apm_package_files.path%TYPE 
);

Package versions need to indicate that they provide interfaces for other software. An interface is an API that other packages can access and utilize. Interfaces are identified as a URI and a version name, that comply with the specification of a version name for package URIs.

-- Add an interface provided by this version.
function add_interface(
    interface_id        in apm_package_dependencies.dependency_id%TYPE
                    default null,
    version_id          in apm_package_versions.version_id%TYPE,
    interface_uri       in apm_package_dependencies.service_uri%TYPE,
    interface_version       in apm_package_dependencies.service_version%TYPE
) return apm_package_dependencies.dependency_id%TYPE;

procedure remove_interface(
    interface_id        in apm_package_dependencies.dependency_id%TYPE,
    version_id          in apm_package_versions.version_id%TYPE
);

procedure remove_interface(
    interface_uri       in apm_package_dependencies.service_uri%TYPE,
    interface_version       in apm_package_dependencies.service_version%TYPE,
    version_id          in apm_package_versions.version_id%TYPE
);

The primary use of interfaces is for other packages to specify required interfaces, known as dependencies. A package cannot be correctly installed unless all of its dependencies have been satisfied.

-- Add a requirement for this version.  A requirement is some interface that this
-- version depends on.
function add_dependency(
    requirement_id      in apm_package_dependencies.dependency_id%TYPE
                    default null,
    version_id          in apm_package_versions.version_id%TYPE,
    requirement_uri     in apm_package_dependencies.service_uri%TYPE,
    requirement_version     in apm_package_dependencies.service_version%TYPE
) return apm_package_dependencies.dependency_id%TYPE;

procedure remove_dependency(
    requirement_id      in apm_package_dependencies.dependency_id%TYPE,
    version_id          in apm_package_versions.version_id%TYPE
);

procedure remove_dependency(
    requirement_uri     in apm_package_dependencies.service_uri%TYPE,
    requirement_version     in apm_package_dependencies.service_version%TYPE,
    version_id          in apm_package_versions.version_id%TYPE
);

As new versions of packages are created, it is necessary to compare their version names. These two functions assist in that task.

-- Given a version_name (e.g. 3.2a), return
-- something that can be lexicographically sorted.
function sortable_version_name (
    version_name        in apm_package_versions.version_name%TYPE
) return varchar;

-- Given two version names, return 1 if one > two, -1 if two > one, 0 otherwise. 
-- Deprecate?
function compare(
    version_name_one        in apm_package_versions.version_name%TYPE,
    version_name_two        in apm_package_versions.version_name%TYPE
) return integer;

Creating Instances of a Package

Once a package is registered in the system, it is possible to create instances of it. Each instance can maintain its own content and parameters.

create or replace package apm_application
as

function new (
    application_id  in acs_objects.object_id%TYPE default null,
    instance_name   in apm_packages.instance_name%TYPE
            default null,
    package_key     in apm_package_types.package_key%TYPE,
    object_type     in acs_objects.object_type%TYPE
               default 'apm_application',
    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 acs_objects.object_id%TYPE;

procedure delete (
    application_id      in acs_objects.object_id%TYPE
);
end apm_application;

Just creating a package instance is not sufficient for it to be served from the web server. A corresponding site node must be created for it. As an example, here is how the OpenACS API Documentation service makes itself available on the OpenACS main site:

declare
    api_doc_id integer;
begin
    api_doc_id := apm_service.new (
      instance_name => 'OpenACS API Browser',
      package_key => 'acs-api-browser',
      context_id => main_site_id
    );

    apm_package.enable(api_doc_id);

    api_doc_id := site_node.new (
      parent_id => site_node.node_id('/'),
      name => 'api-doc',
      directory_p => 't',
      pattern_p => 't',
      object_id => api_doc_id
    );

    commit;
end;
/
show errors

Specifying Configuration Parameters for each Instance

A parameter is a setting that can be changed on a package instance basis. Parameters are registered on each package_key, and the values are associated with each instance. Parameters can have default values and can be of type 'string' or 'number.' There is support with this API for setting a number of minimum and maximum values for each parameter, but for most instances, the minimum and maximum should be 1. It is useful to allow or require multiple values for packages that need to store multiple pieces of information under one parameter. Default values are automatically set when instances are created, but can be changed for each instance.

All of the functions below are in the APM PL/SQL package.

-- Indicate to APM that a parameter is available to the system.
function register_parameter (
    parameter_id        in apm_parameters.parameter_id%TYPE 
                default null,
    parameter_name      in apm_parameters.parameter_name%TYPE,
    description         in apm_parameters.description%TYPE
                default null,
    package_key         in apm_parameters.package_key%TYPE,
    datatype            in apm_parameters.datatype%TYPE 
                default 'string',
    default_value       in apm_parameters.default_value%TYPE 
                default null,
    section_name        in apm_parameters.section_name%TYPE
                default null,
    min_n_values        in apm_parameters.min_n_values%TYPE 
                default 1,
    max_n_values        in apm_parameters.max_n_values%TYPE 
                default 1
) return apm_parameters.parameter_id%TYPE;

function update_parameter (
    parameter_id        in apm_parameters.parameter_id%TYPE,
    parameter_name      in apm_parameters.parameter_name%TYPE,
    description         in apm_parameters.description%TYPE
                default null,
    package_key         in apm_parameters.package_key%TYPE,
    datatype            in apm_parameters.datatype%TYPE 
                default 'string',
    default_value       in apm_parameters.default_value%TYPE 
                default null,
    section_name        in apm_parameters.section_name%TYPE
                default null,
    min_n_values        in apm_parameters.min_n_values%TYPE 
                default 1,
    max_n_values        in apm_parameters.max_n_values%TYPE 
                default 1
) return apm_parameters.parameter_name%TYPE;

-- Remove any uses of this parameter.
procedure unregister_parameter (
    parameter_id        in apm_parameters.parameter_id%TYPE 
                default null
);

The following functions are used to associate values with parameters and instances:

-- Return the value of this parameter for a specific package and parameter.
function get_value (
    parameter_id        in apm_parameter_values.parameter_id%TYPE,
    package_id          in apm_packages.package_id%TYPE         
) return apm_parameter_values.attr_value%TYPE;

function get_value (
    package_id          in apm_packages.package_id%TYPE,
    parameter_name      in apm_parameters.parameter_name%TYPE
) return apm_parameter_values.attr_value%TYPE;

-- Sets a value for a parameter for a package instance.
procedure set_value (
    parameter_id        in apm_parameter_values.parameter_id%TYPE,
    package_id          in apm_packages.package_id%TYPE,        
    attr_value          in apm_parameter_values.attr_value%TYPE
);

procedure set_value (
    package_id          in apm_packages.package_id%TYPE,
    parameter_name      in apm_parameters.parameter_name%TYPE,
    attr_value          in apm_parameter_values.attr_value%TYPE
);  

The central piece of the data model is the apm_package_types table where each package is registered. When a new application or service is installed on an OpenACS instance, a corresponding row in this table is inserted with information about the type of package, e.g. if the forum package is installed on your OpenACS server, a row in apm_package_types will be created, noting that it's an application package type.

The apm_packages table is used to contain information about the instances of packages currently created in the system. The package_key column references the apm_package_types table to ensure that no package instance can be created for a type that does not exist.

The apm_package_versions table contains information specific to a particular version of a package. Several tables reference this one to provide further information about the particular version:

Parameter information is maintained through two tables:

A number of views are available for obtaining information about packages registered in the APM.

The APM's user interface is part of the OpenACS Administration Service. The UI is the primary point of contact with APM by developers and administrators. It is part of OpenACS Administration, because only the site-wide administrator should be able to access it. Thus in order to develop a package, the developer must be granted site-wide administration.

APM has two parameters for configuring how it interacts with the UNIX filesystem, accessible via the Site Map admin page. These parameters need not be changed under most circumstances, but may need to be tweaked for Windows compatibility.

APM has been in production since OpenACS 3.3, and as of version 4.0 offers a stable set of features. One major feature planned is integration with the OpenACS Package Repository for automatic dependency satisfaction. When a user tries to install a package that depends on other packages, the APM will contact the package repository, determine what packages depend on it, and offer the user a chance to download and install them all. This improvement offers value to end users by facilitating the extension of their OpenACS systems.

Architecturally, minor improvements to the data model and the specification file are planned to increase modularity. The current implementation puts all package specification information in a single file. This approach has certain advantages, such as centralization, but splitting this information into several files allows for flexible extensions to the APM architecture over time.

APM packages currently lack provisions to verify security information. There are plans to add MD5 time stamps and PGP signatures to packages to enable secure authentication of packages. These steps are necessary for APM to be usable as a scalable method to distribute packages on multiple repositories worldwide.

Another anticipated change is to split the APM UI into separate systems for authoring, maintaining, and installing packages. The current UI presents all of this functionality in one interface and it can be confusing from a usability perspective.