CSCI 5801 Chapter 5

Generalization

use to manage complexity. Rather than learn the detailed characteristics of every entity that we experience, we place these entities in more general classes (animals, cars, houses, etc.) and learn the characteristics of these classes. This allows us to infer that different members of these classes have some common characteristics e.g. squirrels and rats are rodents.

Sequence Diagrams

used to model the interactions between the actors and the objects within a system

interaction perspective

where you model the interactions between a system and its environment, or between the components of a system.

Structural Perspective

where you model the organization of a system or the structure of the data that is processed by the system

Use case modeling

Each use case represents a discrete task that involves external interaction with a system

Why use graphical Models

1) Facilitate discussion about an existing or proposed system Incomplete and incorrect models are OK as their role is to support discussion. 2) Document an existing system Models should be an accurate representation of the system but need not be complete. 3) Provide a detailed system description that can be used to generate a system implementation Models have to be both correct and complete.

UML Activity Diagram Where does it start? Where does it end? What does the bold lines mean? How about the diamond? What are the boxes? What are the rounded corner rectangles?

1. Start at complete dot 2. end at dot with a circle around it. 3. Bold line means activity coordination. 4. Diamond means a choice/decision will be made. 5. Boxes are systems 6. Rounded corner rectangles are activities

Types of Model

A computation independent model (CIM) These model the important domain abstractions used in a system. CIMs are sometimes called domain models. A platform independent model (PIM) These model the operation of the system without reference to its implementation. The PIM is usually described using UML models that show the static system structure and how it responds to external and internal events. Platform specific models (PSM) These are transformations of the platform-independent model with a separate PSM for each application platform. In principle, there may be layers of PSM, with each layer adding some platform-specific detail.

Context Model

Context models are used to illustrate the operational context of a system - they show what lies outside the system boundaries. Social and organizational concerns may affect the decision on where to position system boundaries. Architectural models show the system and its relationship with other systems.

Models of Existing systems are used during requirements engineering to

Help clarify what the existing system does and can be used as a basis for discussing its strengths and weaknesses.. which leads to requirements for the new system help explain the proposed requirements to other system stakeholders. engineers use these models to discuss design proposals and to document the system for implementation

Model driven Engineering

Model-driven engineering (MDE) is an approach to software development where models rather than programs are the principal outputs of the development process. The programs that execute on a hardware/software platform are then generated automatically from the models. Proponents of MDE argue that this raises the level of abstraction in software engineering so that engineers no longer have to be concerned with programming language details or the specifics of execution platforms.

Usage of model driven engineering

Model-driven engineering is still at an early stage of development, and it is unclear whether or not it will have a significant effect on software engineering practice. Pros Allows systems to be considered at higher levels of abstraction Generating code automatically means that it is cheaper to adapt systems to new platforms. Cons Models for abstraction and not necessarily right for implementation. Savings from generating code may be outweighed by the costs of developing translators for new platforms.

Sequence diagrams

Show interactions between actors and the system and between system components

Activity diagrams

Show the activities involved in a process or in data processing

use case diagram

Show the interaction between a system and its environment

Data Driven models

Show the sequence of actions involved inprocessing input data and generating an associated output

System boundaries

System boundaries are established to define what is inside and what is outside the system. They show other systems that are used or depend on the system being developed. The position of the system boundary has a profound effect on the system requirements. Defining a system boundary is a political judgment There may be pressures to develop system boundaries that increase / decrease the influence or workload of different parts of an organization.

UML

Unified Modeling Language: System modeling now come to mean representing a system using some kind of graphical notation

External Perspective

Where you model the context or environment of the system

Behavioral perspective

Where you model the dynamic behavior of the system and how it responds to events

Behavioral Models

are models of the dynamic behavior of a system as it is executing. They show what happens or what is suppose to happen when a system responds to a stimulus from its environment

Class diagrams

are used when developing an object-oriented system model to show the classes in a system and the associations between these classes. An object class can be thought of as a general definition of one kind of system object. An association is a link between classes that indicates that there is some relationship between these classes. When you are developing models during the early stages of the software engineering process, objects represent something in the real world, such as a patient, a prescription, doctor, etc.

Modeling user interaction

helps identify user requirements

Modeling component interaction

helps us understand if a proposed system structure is likely to deliver the required system performance and dependability

Modeling system to system interaction

highlights the communication problems that may arise

Structural Models

of software display the organization of a system in terms of the components that make up that system and their relationships

Process Models

reveal how the system being developed is used in broader business processes

State Diagrams

show how the system reacts to internal and external events

State Machine Models

show the behaviour of the system in response to external and internal events show the system's responses to stimuli so are often used for modeling real-time systems show system states as nodes and events as arcs between these nodes. When an event occurs, the system moves from one state to another.

class diagrams

show the object classes in the system and the associations between these classes.

Event driven modeling

shows how a system responds to external and internal events

Aggregation Models

shows how classes that are collections are composed of other classes Similar to the part of relationships in semantic data models

System modeling helps..

the analyst understand the functionality of the system and models are used to communicate with customers

System Modeling

the process of developing abstract models of a system, with each model presenting a different view or perspective of that system