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Last modified on 06 Mar 2021

Comp 361 Midterm Review

Requirements Elicitation Models

Domain Model

Describes problem concepts and relationships

This is a UML class diagram.

Use Case Model

Describes different ways actors interact with the system

  • Captures who (actor), what (interaction), and what purpose (goal) without dealing with system internals
    • Note that we may black box our model, and avoid dealing with how actions are executed.
  • Completion will detail all possible ways of achieving goals with the system
  • A use case is a transaction, typically comprised of
    1. Request from primary actor to system
    2. Validation from system for the request & data
    3. Alteration of an internal state by the system
    4. Response from the system to the actor with a result
  • Actor categories
    • Primary - directly interacts with the system
    • Secondary - supports creating values for other actors
    • Facilitator - used by primary/secondary actors to communicate with the system
  • System boundary - definition of what separates the system and its environment
    • Important to have a well defined boundary, as it has a large effect on what should be built

Use Case Template

  • Use case name
  • Scope (affected entities)
  • Level (summary, user-goal, subfunction)
  • Intention in context (description)
  • Multiplicity (scalable situation)
  • Primary actor
    • Secondary actors
  • Main success scenario
    • Sequence & interaction steps
  • Extensions & exceptions
    • Additional/alternative interaction steps

  • Interaction Step either
    • Refers to a lower level use case
    • Describes a base interaction step which
      • Must contain the word System and at least one actor
      • Describe an input (actor to system) or output (system to actor) interaction
    • Describes an optional system processing step or communication step in the environment for clarity
  • Sub steps are denoted with . notation (eg 3.1)
  • Alternate steps are denoted with letters (eg 3a)
  • Parallelism is denoted with ||

Structural Models

Environment Model

Defines the system’s interface (boundaries & operations).

  • Black box view of system
  • Interaction with entities and actors (labelled name:type)
  • Contains arrows and a list of possible input & output methods

Concept Model

Defines the static structure of the system (concepts & relationships)

  • Like an environment model, but showcasing only what is necessary to create the system interactions
  • Cards may be grouped to show the system/object for which they belong to

Dependency Model

  • Usage dependency - dashed arrow with <<use>>
    • <<call>>, <<instantiate>>, <<parameter>>
  • Transient references pass by parameters - dashed arrow pointing from caller to parameter
  • Navigation represent accessibility - solid arrow pointing from reference holder (with count: 0..c) to reference, with the name as the annotation; note that this association can be bidirectional
  • Composition arrows (from holder to reference) is used to represent associations where the reference cannot live outside the existence or timeline of the holder
  • References that cannot be changed can be annotated with {frozen}

Behavioural Models

Operation Model

  • System operations may
    • Create a new instance of a class
    • Remove an object from system state
    • Change attribute value or an existing object
    • Add/remove link to/from association
    • Send message to actor

Operation Schema

  • Operation - Caller::methodName(arg0: arg0Type, arg1: arg1Type, ...)
  • Scope - classes & associations from concept model
  • Message - all message output types - Sender::{msgs, here};
  • New - all objects that may be created - newX: X
  • Pre - (optional) conditions that must be met for this operation to make sense
  • Post - description of effects of operation

Protocol Model

Defines allowable interactions between system & environment

  • Denoted using use case maps
  • Elements
    • Start node - black dot
    • End node - black bar
    • Responsibility - annotated x
    • Or - fork
    • And - two bars with three arrows in between
    • Stubs - white diamond
  • Conditions added on paths with brackets
  • Responsibilities may be surrounded by box dictating entity
  • Stubs may have multiple annotated out paths
  • Can use timers, with either an input condition (dot is filled) or an output timeout value (dot has clock symbol, timeout line is jagged)

Communication Design

Compact model for simple flows

  • Dewey decimal for sequencing and concurrency
  • * to represent repetition
  • var := method() to represent return
  • ' or many 's to represent switch cases

Sequence Diagram

Sequence of messages between objects

  • name:type with lifelines
  • Optional * to denote many (method calls or objects)
  • Objects can be created/destroyed during execution, denoted with {new} and {destroyed}. Those created then destroyed are {transient}
  • Destruction at the end of an execution is denoted by a cross on the lifeline