Problem Analysis and Structure Models and Frames

Solutions Traditional focus on solutions Little attention paid to problems to be solved Structured methods usually deal entirely with solutions –Problem is inferred from the outline solution

Problem Frames A mechanism for problem analysis and structuring Avoids solution-oriented thinking PFs characterise classes of problems that commonly occur as subproblems of larger, realistic, problems. Use a process of decomposition This is not top-down/func. dec.

Key concepts World Phenomena Domains Descriptions

World Problems such as controlling lifts, bank accounting, theatre reservations, car brake controllers, libraries are all located in the world. The computer is the solution

Phenomena Analysis conerned with the World and its phenomena PF phenomenology includes: –Entities –Events –Values –States –Truths –Roles Controllable phenomena

Domains A domain is simply a distinct part of the world A collection of related phenomena Phenomena & their relationships constitute domain properties Domains can share phenomena –Lift & passengers interact because pressing a button is a shared phenomenon Machine domain is the solution

Descriptions Problem analysis concerned with these descriptions over the phenomena of the problem domain: –the Requirement –the Domain Properties –the Machine Specification Development success: MS, DP  R

Problem Frames: Elementary Real problems are not general but specific A frame captures characteristics of a very constrained class of idealised (simplified) problems Stipulate structure and charac. of requirement, of the domain (possibly several), and of interfaces among domains

Frame Diagrams Striped box = the machine to build Plain box = part of the world that interacts with the machine Solid line = interface of shared phenomena Ellipse = requirement Dotted arrow shows req is a description of the phenomena of the world principal parts & solution task

Simple Behaviour Frame Simple control problem Requirement (RB) is to impose certain behaviour on the problem domain (CD) Req. expressed in terms of shared phenomena C3

Simple Information Answers

Simple Information Display

Simple Workpieces Frame

The JSP Frame

JSP Frame continued Tightly constrained frame –Clear rules for checking if each step has been done correctly. –If you can’t complete a step, you can find the reason Streams & correspondences can’t be described = frame misfit Can’t form program structure (st. clash) If a misfit, then try another frame, and another method.

Exercises For each of the following problems, find a suitable frame and draw a frame diagram –A system to control automatic ticket machines at a roadside toll booth –A signal processing program in which input signals have to be processed and converted and then output –A small interactive editor that will be part of a Personal Information Manager

Further Reading See the web site for pointers to more detailed information