Boundary, Control, and Entity Classes: 25-Comp-B11 Advanced Software Design, December 2019, Q19

Question 19 of 28: Boundary, Control, and Entity Classes

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

17-Comp-B11 Advanced Software Design — National Exams, December 2019. 3 hours, closed book exam with one aid sheet allowed (written on both sides), no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any five (5) questions in Part I, any three (3) in Part II, any four (4) in Part III, any two (2) in Part IV, and any five (5) in Part V — only the first questions answered, in each part, as they appear in the answer book are marked. All questions carry equal weight, so the 19 questions actually marked (5+3+4+2+5 of 28) each count for 100/19 ≈ 5.26% of the paper. All 28 questions are answered below for completeness.

Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, design principles, testing, dependability; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process and quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — creational/structural/behavioural pattern catalogue and the "program to an interface, not an implementation" / "favor object composition over class inheritance" principles; Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, visibility, and multiple inheritance semantics; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/class invariants; Barbara Liskov's 1987 substitutability paper for Question 12; Karl Wiegers, Software Requirements (3rd ed.); Myers, The Art of Software Testing, for Question 6.

PART I — General Principles (answer any 5 of 7)

Question 19: Boundary, Control, and Entity Classes (Part IV)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Boundary classes model the interface between the system and its actors — screens, forms, APIs. Control classes coordinate the workflow of a use case, mediating between boundary and entity classes without themselves holding persistent data. Entity classes model persistent domain data and the business rules attached to it.

Separation of concerns. Boundary classes are, by their nature, VOLATILE — they change whenever the presentation technology changes even when the underlying business logic and data are completely unchanged. Keeping Boundary separate from Entity (persistent domain data) and Control (use-case orchestration) confines presentation-layer churn to the Boundary classes alone, so a UI framework upgrade never forces re-verifying business logic that merely happened to live inside now-obsolete UI classes.

GUI design is the concern of the Boundary classes specifically — they are the only one of the three types that touches presentation technology at all.

Illustration (Question 4's application). TransactionView (Question 18) is a Boundary class — it renders the transaction list and forwards user actions. FinanceController/TransactionManager are Control classes — they orchestrate add/edit/calculate/save/load without themselves being persistent data. Transaction is an Entity class — it holds the persistent amount/date/category data and is exactly the object FileStorage serializes.