At the Forge - Bricolage

This command downloads and installs necessary modules from CPAN, tests the Bricolage installation to ensure that it is working right and, if all went well, installs Bricolage itself.

It's easy to run into some problems when installing Bricolage, but overall the installation was impressively easy, given the complexity of the system. The Makefile offered intelligent defaults, forced me to provide a password to the “bric” PostgreSQL user and generally ensured that things were running correctly and smoothly.

Once everything was installed, I invoked bric_apachectl start to start Apache, pointed my Web browser at the root directory and was greeted with a screen asking me to log in. The installation had succeeded. As suggested by the Bricolage documentation, I immediately changed the administrative password, which is appropriately set to “change me now!” by default.

At this point I should mention that Bricolage uses a fair number of pop-up windows. I personally happen to dislike pop-ups, even when they are not used in the context of advertising. Although I understand the nature of user interfaces in HTML often requires pop-ups for the natural flow of information, I still wish Bricolage used them a bit less. Moreover, a number of the internal links depend on JavaScript, which means I cannot use my beloved middle mouse button to open a new tab instead of a new window. But, this and other minor blemishes do little to change the fact that Bricolage is truly an amazing package.

Bricolage consists of several parts: a data model in PostgreSQL, a number of Perl modules and a number of front-end templates that display information retrieved by the modules. In this way, it is similar to other sophisticated database-backed systems. Indeed, although Bricolage attempts to solve a more limited set of problems than OpenACS does, and obviously uses different technologies to accomplish its goals, the separation of data, libraries and templates is quite similar to that system and to many other systems using a three-tier architecture.

If you look in the inst directory of the Bricolage package, you see the PostgreSQL database definitions used by the system. If you are new to PostgreSQL, you might be a bit surprised by some of the things you see there, such as sequences and constraints.

Sequences are a special kind of numeric object in PostgreSQL whose values can never be reused. They are most often used to ensure that IDs in the system are unique, especially when used as primary keys. If you define a PostgreSQL column to be SERIAL rather than INTEGER, you actually are creating a sequence behind the scenes. Older versions of PostgreSQL made it inconvenient to drop a table with a SERIAL column; you had to drop the table and then drop the sequence associated with the SERIAL column as well. As of PostgreSQL 7.3, however, removing a table automatically removes any sequences that were associated with its SERIAL columns.

Constraints allow the database to reject INSERT and UPDATE statements that set values outside of a particular range. For example, Bricolage defines a media table in which every element has a priority between 1 and 5 but a default of 3. The column definition thus looks like:

priority   NUMERIC(1,0)  NOT NULL
                         DEFAULT 3
                         CONSTRAINT ck_media__priority
                         CHECK (priority BETWEEN 1 AND 5)

The constraint can be given an optional name, in this case ck_media_priority. This makes it easier to find and fix errors; if you try to insert an invalid value into this column, PostgreSQL indicates the name of the violated constraint. This helps quite a bit when debugging problems with the database definition as well as with the applications using the database.

Also a bit surprising is that a small number of functions are defined. PostgreSQL makes it possible to define functions in a number of different languages, including standard SQL and the procedural Pl/PGSQL, as well as database-enhanced versions of Perl, Python and Tcl.

Of course, the core of the Bricolage data model is the tables. A person table is used to describe system users, an org table describes organizations and then a person_org table handles the intersection between these two tables.

Indeed, it's possible to achieve a good understanding of what's happening inside Bricolage without too much difficulty by simply looking at the database definitions. For example, I added a new story—a glowing review of Core Perl—to Bricolage using the default administrative user account with all of the defaults. This inserted a new record into the story table, assigning it a priority (as we saw above), a date of publication and expiration, a version number (as Bricolage also handles versioning of articles) and an indication of whether the story has been published.

Several keys foreign to other tables demonstrate how this particular article fits into the system. We can see it was created by the administrative user, because the usr column points to the usr table; it is part of the story workflow, distinct from other workflows that have been defined, and referenced in a foreign key from the workflow__id column; it came from the edit desk, distinct from other desks, such as copy, legal and publishing, and referenced with a foreign key to the desk table; and it is considered to be a book review element, because its element__id column points to the element table. Each of these other tables is connected to still other tables that provide additional auxiliary information, from burners to group IDs to formatting information.

In short, the story table sits close to the center of the Bricolage data model—just as it should be given that a CMS is centered around content, of which stories are the primary example. Indeed, if you are new to the world of relational databases or want to see an open-source project that uses them in a sophisticated way, you would do well to look at Bricolage.