System Modeling and Perspectives

System Modeling

• System is an integrated set of elements achieving a defined objective.
• System modeling develops abstract system models, each presenting a specific viewpoint or perspective
• Representing a system using graphical notation, commonly UML, has becoming synonymous with system modeling
• System modeling aids analysts understand system functionality, and models facilitate customer communication

Existing and Planned System Models

• Models of existing systems are used during requirements engineering
• They help clarify the existing system's functions and serve as a basis for discussing strengths, weaknesses, and new system requirements
• Models of new systems help explain proposed requirements to system stakeholders,
• Engineers use models to discuss design proposals and document systems for implementation
• In model-driven engineering, complete or partial system implementations can be generated from system models

System Perspectives

• Different models can represent the system from different angles
• External perspective: Models the system's context and environment.
• Interaction perspective: Models interactions between the system and its environment, and among system components
• Structural perspective: Models organizational structures of systems and the organization of data.
• Behavioral perspective: Models a system's dynamic behavior and response to events.

Unified Modeling Language (UML) Diagrams

• UML diagrams are based on the UML and visually representing a system as well as main actors, roles, actions, artifacts, and classes
• This is to better understand, alter, maintain, or document system information
• UML diagram types include activity, use case, sequence, class and state diagrams

UML Diagram Types

• Activity diagrams illustrate activities within a process or data processing
• Use case diagrams illustrate interactions between a system and its environment
• Sequence diagrams illustrate interactions between actors, the system, and system components.
• Class diagrams illustrate object classes in a system and their associations.
• State diagrams illustrate how a system reacts to internal and external events

Use of Graphical Models

• Facilitate discussion about existing or proposed systems and they can also support discussion even if incomplete
• Document an existing system, and they should be accurate but need not be complete
• Describe a system in detail to generate a system implementation, in this case it has to be both correct and complete

Context Models

• Context models illustrate a system's operational context and what's outside system boundaries
• Social and organizational concerns impact decisions on placing system boundaries
• Architectural models illustrate the system and its relationship with other systems

System Boundaries

• System boundaries define what's inside and outside the system.
• Also show other systems employed or depended on in the system being developed
• The position of the system boundary impacts system requirements
• Defining a system boundary is a political decision under pressure to maximize influence or minimize workload on different organizations' parts

Process Perspective

• Context models show other systems in the environment, but not how the target system is used
• Process models expose how the system in focus fits into bigger business processes
• UML activity diagrams define business process models

Interaction Models

• User interaction modeling identifies user requirements
• System-to-system interaction modeling reveals potential communication issues
• Component interaction modeling reveals if system structure delivers desired system performance
• Use case and sequence diagrams can be for interaction modeling

Use Case Modeling

• Use cases support requirements elicitation and are now in the UML
• Each use case represents a discrete task with external interactions to a system
• Actors may be people or other systems
• An overview can be shown diagrammatically as well as in detailed text form

Sequence Diagrams

• Sequence diagrams are part of UML to model interactions between actors and objects within a system
• Shows the sequence of interactions in a particular use case
• Objects and actors are listed at the diagram's top, with vertical dotted lines
• Interactions are shown with annotated arrows

Structural Models

• Structural models show a system's organization regarding components and relationships
• These may be static models as it relates to system design, or dynamic models when the organization is executing
• These models are created you are discussing and designing the system architecture
• Class diagrams are the most used structural model for modeling the static structure of object classes

Class Diagrams

• Class diagrams are used to develop object-oriented system models to represent classes and associations
• An object class provides is of a general definition of system objects
• An association is a link signifies a relationship between classes
• Early in software engineering, objects represent real-world things like patients, prescriptions, doctors etc.

Generalization

• Generalization manages complexity daily
• Rather than memorizing details of every entity, entities are put in general classes (animals, cars, houses) and then learn the characteristics of those classes
• This infers that members of these classes share some characteristics e.g. squirrels and rats are rodents

Object Class Aggregation Models

• Aggregation models show how classes as collections are composed of other classes
• These models relate similarly to "part-of" relationships in semantic data models

Behavioral Models

-Behavioral models are of a system's dynamic behavior while executing

• They show system responses to environmental stimuli
• Stimuli can be data which system processes
• Events that trigger processing, possibly with related data

Data-Driven Modeling

• Many business systems are data-processing systems, primarily data-driven
• They're driven by data input into system with very minimal external event processing
• Data-driven models shows the sequence of actions in processing input data to generate output
• The model is used in requirement analysis because they can show end-to-end processing

Event-Driven Modeling

• Real-time systems are often event-driven
• Event-driven modeling exhibits response to external and internal events
• Assumes a system has a finite number of states and events cause transitions from one to another

State Machine Models

• Model system states and system behavior in response to external and internal events
• Showcase system responses to external stimuli
• State machine models display system states as nodes and events as arcs through nodes
• Statecharts are UML components and are used to model state machines

System Design

• The chapter moves onto discussing system design

System Engineering

• System is an integrated set of key elements that helps to achieve the goal
• An interdisciplinary field combining engineering and engineering management
• It focus on how the systems are designed, and managed throughout their life cycle
• A system might be described in a broad way that includes - Logical Functional: What the system is intended to do - Physical Features: How the system aspects look, how it is produced

System Design

• A design represents the product or the system with enough details included to enable it's implementation
• Process of designing architectures, components and interfaces for a system to meet the requirements
• Can be considered using systems theory to produce development
• Model includes data, architecture, interface, component design

Architectural Design

• This process aims at determining the sub-systems to make up as system and the subsystem control as well
• The architecture helps facilitate how the software was designed
• Identifying what hardware and software components make up the system to form a development framework

Architectural Design Cont..

• Helps with the system decompose into interaction system
• Defines relationships among the main structure elements
• The output helps describe the software architecture

Architectural Design Cont..

• Architectural design is part of the early stages of the design process
• Block diagrams are used by defining an overview of the system to understand the feature of all the key components
• This often occurs in part with specific activities
• It allows to link the specifications through to the design process
• It includes identifying the major components and communications within
• The architecture of the Robot Control system

Architectural Abstraction

• Used when the architecture is at a smaller scale concerns about individual program
• The program components are decomposed within these programs
• Large scope architectural issues include complex enterprise systems with programs
• These types of services are delivered through different channels over different computers

Architectural Design Cont..

• Advantages are to have explicit designed to have a better software architecture
• Stakeholders: The architecture being used can help stakeholders with communication
• System analysis helps the system to meed all the non-functional requirements
• Large-scale reuse and helps the product to be better developed

Architectural Representation

• A frequently used method to document is simple blocks diagrams that helps show all the relationship between different entities
• It has been criticized because the - diagrams lack semantic structure - don't show how entities relate to each other

Box and Line Diagram

• Boxes within the diagram help show components that have been decomposed
• Arrows are used to define how data is transmitted or what control signals are passed between components in the direction the arrows are pointing towards
• It's abstract and does not how visible properties related
• They are useful for communicating ideas to relevant stakeholders

Architectural Design Decision

• Creative process where design help helps a system reach functional and non-functional needs
• Its a creactive processed that allows it to work differently based on different needs
• It affects the non-fundamental characteristics of the system

Architecture and Systems Characteristics

• Based on the close relationship to non-functional and software architecture
• Certain architectural structures must be implemented for the system
• Performances can be localized
• Security can be localized within layers

Architectural Safety

• Safety measure must localize safety features for the sub-system
• Availability features must include redundancy
• Maintainability includes using fine-grain replaceable components

Architectural Views

• A four fundamental views must be considered as architecture views - Logical overview - Process Overview - Development Overview - Physical Components
• To properly relate use case one must consider scenarios

Architectural Patterns

• Use patterns are a means to represent and share knowledge
• Stylized design is tried and tested in different environment
• Pattern included different information that one they are used in and not useful in
• Can be represented using a tabular graph design

Layered Architecture

• It models that each sub-system is connected to the the interface of the actual system
• This allows different abstractions, machines be be more specific and set layers of services
• When any lay interface this allows that one adjacent layer to be impacted
• It is often useful in structure system for this way

Repository Architecture

• Sub-System allows that data be exchanged in two ways - The data is accessed to one central database and can be used by the subsystem - Maintain data but the subsystem must be explicitly accessed
• If there is a amount data used the repository must be explicitly used

Client-Server Architecture

• The data processing must be distributed with in range of components
• It can implemented on a single computer
• It is set with stand-alone servers but it can do a variety of things
• The network allows clients to access servers

Applications Architectural

• Applications are designed to help an organization meet its' needs
• Business has many things in common
• generic architecture system helps with system data be modified

Application Types

• Data processings applications process in batch
• Transactions processing is data focused
• The events processes actions based in events
• Formal language specifies languages

Transaction Applications

• E-Commerce
• Reservation systems

Language Architecture Systems

• Compilers
• Command Interpreters

Transaction Processing System

• The process requests help the user better be informed and access data from the database
• User must make an asynchronous request
• The process must be made from transaction manager

Software architecture ATM system

• There are 3 key components - input - process - output

Information System Architecture

• This system has a generic architecture but needs to be layered
• The action must be transaction based, the database needs to be up to date
• The must include
  • interface
  • communications
  • access data
  • system data

Internet Web System

• This system must be modeled using the approach system to create and better interface
• Layers allow for a more customized access into Internet base
• The server architecture also must include a multi-tier style to better function

Multi-Tier Design

• Web sever
• Layer applications
• Databases

Language Processing System

• It help the computer understand a natural language and understand it
• Act on the instruction the language uses
• Althirhtms are are used better access data