Model Domains and Real Worlds Book: Problem Frames: Analyzing and structuring software development problems Author: Michael Jackson Presenter: Ryan Waggoner

About Michael Jackson Has over 39 years experience in the software development industry Created the JSD method of system development and JSP method of program design - a government standard Honorary doctorate, Stevens award, IEE achievement medal, and BCS Lovelace medal Currently works as an independent consultant and part-time researcher at AT&T Research

General Model - a distinct domain that corresponds by analogy to the real world domain in an information problem Model domain separates and makes explicit some private phenomena of the information machine: the set of variables it uses to compute its display outputs Split the problem into two sub problems: one builds the model, and the other uses it

Phase 1: Building the Model Real World - Part of the world which information is required Display - domain where information is shown Objective is to ensure that the Display correctly matches the Real World information by using symbolic phenomena to correspond to casual phenomena. Take the real world situation and break the problem into variables. In simple models, no variables are needed, but when any level of complexity is added to the problem, variables become essential. Look at each of the variables as separate model domains to determine their requirements to function properly in correspondence with real world information. Gradually increase complexity. Identify model variables. To be a model variable, which are vestigial models of the real world, they must meet two conditions: Correspondence requirement and Common Description

Phase 2: Introducing Model Domain Model Domains aren’t part of the original problem, but are part of the solution. Break the model into two separate sub problems - Break the direct correlation between the Display(symbolic phenomena) and Real World(casual phenomena) by separating them and correlating each of them a model phenomena: SP CP into SP MP and MP CP Build two separate models. One that connects the Real World to the Model, and one that connects the Model to the Display. Designing Model - After determining correspondences, define model operations, and symbolic states that correspond to the real world. Develop the structure. Goals - Reduce space and response-time

Advantages Machine can remember phenomena from the past Machine can carry out burdensome incremental calculations Can model and maintain the values of defined terms Can model process of a conceptual domain as if they were physical entities Can capture and embody inference rules Can provide surrogates for private phenomena that are inaccessible to the machine

Concerns Model Imperfection Time Lag Incompleteness Errors