James Martin CpE 691 February 4, 2010

 Problem Overview  The pattern solution  Comparing patterns and decision  The pattern-decision relationship  Using patterns  Limitations and further research 2

 Decisions made during software architecting have a substantial impact on the system  Design decisions aren’t documented by architects thoroughly enough by architects. ◦ All aspects (i.e. alternatives, rationale, expected consequences, etc) are not usually captured  Leads to “knowledge vaporization” 3

 Decisions are not recorded  Development and evolution cycles of software do not have appropriate access to decisions that were made during the architectural design  The decisions might reside in the heads of architects, but people eventually forget  “If something is not written down, it does not exist” 4

 It takes a lot of effort  Decisions are made without thought  Can be disruptive to the flow of design  Architects don’t know how 5

 A.K.A. architectural style  Patterns help document decisions because they: ◦ Include general structural and behavioral info ◦ When a pattern is chosen, a decision is made so it can be documented ◦ Architects already use patterns so they aren’t disruptive ◦ Patterns are typically easy to follow ◦ They are solutions to recurring problems 6

 Layers  Pipes and filters  Blackboard  Model-View-Controller (MVC)  Presentation-Abstraction-Control (PAC) 7

 Issue being decided  Decision that was made  Alternatives  Reasons for making the decision 8

Pattern sectionDecision Section Name ProblemIssue CategoryGroup Status ContextAssumptions, constraints Solution variants according to forcesPositions SolutionDecision RationaleImplications Resulting context / consequences Example, know issues Related patternsRelated decisions, requirements, artifacts, or principles Notes 9

 Two types of knowledge 1.Application-generic knowledge  Implicate knowledge gained through previous experiences (such as from patterns)  Used to make decisions 2.Application-specific knowledge  Involves decisions made during the architecting process, as well as the solutions  It is the decisions  Patterns comprise #1  Decisions comprise #2 10

 Architecting is decision-intensive  Making a lot of decisions means doing a lot of documentation  Using patterns helps alleviate the need for as much documentation since the documentation is implicit  When a pattern is selected the architectural decision is documented via the pattern’s usage 11

 Application specific decisions must still be documented  Not all decisions can be captured via patterns ◦ Organization decisions ◦ Financial decisions  Using multiple patterns together without understanding them can lead to conflicts  Why a decision was made is not documented via patterns 12