Prescriptive Process Models Jon Walker

Prescription? What does prescriptive mean?

Answer ● Proscribe a set of process elements ● “Things to do” ● A model of the lifecycle also

Software Life-Cycle Models ● Build-And-Fix  Build and product without any specification or design  Modify (or “fix”) product until client is satisfied

Waterfall ● Used exclusively until the early 80s ● Output (or “artifacts”) from each phase go into next phase ● What are artifacts? ● What are the advantages of Waterfall?  Forced discipline of going through each phase  Well defined phases ● What are the disadvantages?  No modeling of requirements  Traceability is hard to attain (why?)

Incremental Models ● RAD ● Incremental

RAD ● Rapid Application Development (RAD) ● Short development cycle ● High speed waterfall ● Break into pieces/components ● Assign teams to components ● What do you think the pros/cons are?

Pros/Cons ● Pros of RAD  More rapid feedback than waterfall ● Cons of RAD  Project has to be scalable ● Able to be broken into pieces  For a large project you need to have a lot of teams  May not be appropriate if there is a lot of technical risk (interfaces change)

Incremental ● Break the software into pieces ● Build and test the software after adding each piece (incrementally) ● Stop when the final product meets the specifications ● The product must be testable as each piece is added ● What do you think the pros/cons are?

Pros/Cons ● Pros of Incremental  Client gets a functional product earlier  Change in requirements can be handled incrementally ● Cons of Incremental  Product has to naturally break into pieces that can be incorporated one at a time without breaking existing functionality  Quickly degenerates into build-and-fix model

Evolutionary ● Rapid Prototyping ● Spiral ● Synchronize and Stabilize

Rapid Prototyping ● Build a prototype and refine prototype until the customer is satisfied ● What are the pros/cons?

Pros/Cons ● Pros of Rapid Prototype  Requirements are more likely to be correct  Input from prototype can be used in design ● Cons of Rapid Prototype  Problem with seeing prototype as throw- away?  Design may be inflexible  Difficult to review decisions made during certain phases

Spiral ● Incorporates aspects of the other models ● Main objective is to reduce risk  What is risk? ● Like Waterfall but risk analysis is done before each phase and verification is done afterwards ● What are the pros/cons?

Pros/Cons ● Pros of Spiral  Emphasis on alternatives so when a problem is encountered another approach can be taken ● Cons of Spiral  Requires that developers are good at identifying and mitigating risks

Synchronize and Stabilize ● Variation on Incremental model ● Gather requirements ● Prioritize and break into three or four builds with the earlier builds having the most important features ● Features are worked on by a number of independent teams ● Each day or periodically during the lifecycle  “Synchronize” all source code  Test, debug, and “stabilize”  “Freeze” result ● Used by Microsoft ● Advantages and disadvantages are similar to incremental model

Specialized Process Models ● Component-Based Development  Like spiral  Identify components at start of each cycle ● Formal Methods  Mathematical specification of software ● Aspect-Oriented Development  Extract system wide features  Aspect oriented languages

Rational Unified Process (RUP) ● James Rumbaugh, Grady Booch, Ivar Jacobsen  Had individual methods for developing software  Rumbaugh and Booch ● 1990 – unified method ● Added Jacobsen - requirements ● Considered the “modern” alternative to waterfall ● Standard for OO software development ● Phases much like waterfall ● Defines work products or “models” for each phase  e.g. Use cases

Phases of RUP ● Phases  Inception  Elaboration  Contruction  Transition  Production ● What are the waterfall phases again? ● Can you match them? ● Difference is that they happen in increments ● Increments may be concurrent