Legacy Database Replacement with LAMP

BRAD was built on a server running LAMP, and it seemed obvious that we should use open-source PHP classes in its development. PHP Extension and Application Repository (PEAR) modules were used for database access, form generation and processing and basic error handling. An existing error class was modified to warn of an error but hide the full message from the user.

Whenever I needed a particular function, I went looking for an open-source module before writing my own. Doing so dramatically sped up the development cycle (see Table 1 for a list of modules used in BRAD).

Because the BRS system had been around for so long, staff had refined their use of the system to a high degree. BRS did have a powerful and fast search facility. It was able to search for particular words in all or any fields specified by the user. Some quirks had to be overcome, however, such as stop words, words not indexed. These included complete names of some musical groups, The Who being one example. In this particular case, to find items by The Who you have to know something else about the group, such as one of the members (Pete Townsend) or something they wrote (Tommy). Neither approach always was reliable.

The sometimes unexpected behavior and the difficulty of using a command-line interface meant that most staff used the music librarian to find items, simply presenting a handwritten list of requests. Among the expectations for the new system were an equal or better search capability and a simplified interface that could be used by anyone with minimal training.

One of the most powerful features of BRS was that you could limit search terms to certain fields, for example:

Mozart.cp. piano

would return anything with Mozart in the composer (cp) field and piano in any field. We decided to retain this syntax in BRAD so that power users still could do the kinds of searches they were used to doing. We had planned to add an advanced search page for BRAD; however, this syntax has turned out to be so flexible that we haven't needed it.

We faced several challenges with the project. Most of them had to do with modifying MySQL's default behaviors to suit our requirements. The first challenge was to remove all stop words—the list of words not indexed by MySQL due to their presumed commonality in the data. In our situation, every word is considered important.

In MySQL, removing stop words is achieved simply by adding the following line to the MySQL configuration file before adding anything to the database:

ft_stopword_file = ""

The second challenge was to allow searches for words smaller than the four-character limit typically used by MySQL. The BRS system indexed every word regardless of size, apart from those listed as stop words, and removing all stop words would make any search results more in-line with the terms entered.

This problem was solved by doing two things. First, we reduced the index word size to three characters by adding the following to the config file:

set-variable = ft_min_word_len=3

Because of the amount of data, these settings were considered to be acceptable performance trade-offs.

The second thing we did was implement a smart query engine that adapted the query, depending on the shortest word in the search terms, before sending it MySQL. This allows full-text searching regardless of the length of any search term.

The last challenge was to make all searches AND by default. MySQL's boolean full-text mode is an OR search when no modifiers are used. You normally would add a + before each term to make it an AND search. The query engine was built to add the + automatically when no other modifier is present.