Content Types

ETP Content Types

Standard page attributes

The content repository data model (a standard part of OpenACS 4) primarily keeps track of content items , each of which may have multiple content revisions . The content_revision object type refers to a row in the cr_revisions table. Each revision contains the standard attributes of the pages you create with ETP, such as Title, Description, and Content. Additionally, the standard acs_object attributes are stored for each revision, such as the creation date and creating user.

Referring back to the definition of the default ETP application, you'll notice that it specifies that the etp_page_revision content type is to be used for the index page and for all content pages. etp_page_revision is a subtype of content_revision, but does not add any additional attributes. It is just for easier integration with the search package. The page templates used by the default application may refer to only the standard page attributes stored in the cr_revisions table.

Extended page attributes: why do we need them?

The standard page attributes, while providing all the basic functionality for a collaboratively edited website, are rarely sufficient to implement real world designs.

Imagine you're creating an online scientific journal. The graphic design mockup shows you that each issue of the journal contains a table of contents listing all the articles in that issue. However, the table of contents is organized into multiple sections: Editorial, Research, Corrections, and so on. You also notice that the design assumes that each journal issue has a distinguishable publication date, and that each journal article has a distinguishable abstract (a quick summary of the writers' findings which can be skimmed or searched).

All the standard page attributes (Title, Description, Content, etc.) are still useful, but in order to provide the structured data elements implied by the journal templates, we need to define some extended page attributes. In particular, we know that journal issues need to have a publication date, and journal articles need to have a section and an abstract.

Defining a new content type

Creating a new content type is done by calling the


etp::define_content_type

procedure from one of your tcl library files. Here's how you would accomplish the journal example discussed above:

etp::define_content_type journal_issue "Journal Issue" "Journal Issues" {
    { publication_date "Publication Date" "Publication Dates" string "size=60" "" }
}

etp::define_content_type journal_article "Journal Article" "Journal Articles" {
    { section Section Sections string "" "" }
    { abstract Abstract Abstracts string "rows=24 cols=80" "" }
}

The first 3 parameters to define_content_type are the internal name of the content type, the name to display, and the plural form of that name. The fourth parameter is a list of records describing each extended page attribute. Each record is a list containing the following values (in sequence):

attribute_name
pretty_name
pretty_plural
datatype (must be one of the entries in acs_datatypes: string, boolean, number, integer, date, etc.)
html (a string containing html attributes for the input control. useful attributes are "size=X" to specify the size of standard input controls, and "rows=X cols=X" to specify the size of a textarea. Textareas will be used only if the datatype is string and html specifies rows or cols.)
default_value (can either be a string denoting a single default value, or the name of a callback function you've defined in the etp namespace which is used to provide values for select lists).

Once you've defined a content type, you may refer to it when calling the etp::define_application procedure to set up a new application. To continue with our journal example, you'd want to do this as follows:

etp::define_application journal {
    index_template                www/templates/journal-issue
    index_object_name             "Journal Issue"
    index_content_type            journal_issue

    content_template              www/templates/journal-article
    content_object_name           "Article"
    content_content_type          journal_article
}

Creating the templates that make use of your custom content types is the subject of the next page . After that's been done, the authors of the journal will be able to create a new issue of the journal simply by creating a new instance of the ETP package (a process that's automated within the ETP interface by the "create subtopic" command) and ensuring that the new content section is using the journal application. This setup can be automated, since it's possible to specify the application to use for any subtopic created within a particular directory.

luke@museatech.net