Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions (Addison-Wesley Signature Series (Fowler))

by Hohpe Gregor

When discussing Pipes and Filters architectures, we need to be cautious with the term filter. We later define two additional patterns, the Message Filter (237) and the Content Filter (342). While both of these are special cases of a generic filter, so are many other patterns in this pattern language. In other words, a pattern does not have to involve a filtering function (e.g., eliminating fields or messages) in order to be a filter in the sense of Pipes and Filters. We could have avoided this confusion by renaming the Pipes and Filters architectural style. However, we felt that Pipes and Filters is such an important and widely discussed concept that it would be even more confusing if we gave it a new name. We are trying to use the word filter cautiously throughout these patterns and trying to be clear about whether we are talking about a generic filter as in Pipes and Filters or a Message Filter (237)/Content Filter (342) that filters messages. If we thought there might still be confusion, we called the generic filter a component, which is a generic enough (and often abused enough) term that it should not get us into any trouble.