The Components Of A System

Published Date: 02 Nov 2017

Object Diagram

An object diagram illustrates the relationship between objects of a class at a particular instant in time. A collection of object diagrams provide useful insight on how a certain aspect of the system is meant to evolve. They typically serve as examples for class diagrams; because objects are specific entities, object diagrams hold more information than class diagrams.

Package Diagram

A package is a mechanism for grouping related modeling elements (classes, interfaces, diagrams etc.). A package diagram shows the organization of model elements and the relationship between packages in a system.

Profile Diagram

A model, in software engineering is a visual representation of phenomena in the real world. A meta-model is a model which represents properties of the model itself.

Behavioral UML Diagrams

Use-Case Diagram

A use-case

diagram is a visual representation of the functional requirements of a software system. It follows the different users in a system (actors), the various system functionalities (use-cases) and the elements responsible for implementing these functionalities.

Activity Diagram

An activity model emphasizes on execution and flow of control of a system. While interaction diagrams show the flow of messages from one object to another, activity diagrams focus on the message flow between activities.

Interaction Diagram

An interaction diagram focuses on how the different objects of a system communicate. There are 4 types of interaction diagrams, namely: Sequence Diagram, Communication Diagram, Timing Diagram and Interaction Overview Diagram (John, 2000).

Sequence Diagram

This is a visual representation of the order of operation between processes within a given time period. It shows the existing classes in a particular use-case scenario and the sequence in which messages between them are exchanged. Because they provide a snapshot of what happens within a given period, sequence diagrams enable the identification of missing elements in a system. A drawback to this however is that one diagram on its own is incomplete, and there is no definite number of diagrams that comprise a design. The number is determined by the experience of the designer.

 

Communication Diagram

This model also represents the sequence in which messages between objects are exchanged. The difference however, lies in the presentation. Communication diagrams emphasize the nature of the interaction between elements, while sequence diagrams show better the order in which the interactions take place.

Timing Diagram

A timing diagram represents the behavior of a set of objects within a given time constraint. It can be used to view the change of state of a set of elements over a

given time period as well as the interaction between a given set of timed events.

State Machine Diagram

This is a chart which can be used to depict various types of systems, whether computer or business related. It depicts the life-cycle of a given object, describes the different states that object assumes during its life-time, the cause of transition between states and the resultant actions of this transition (Fowler, 2000). UML state machines however, are not purely diagrammatical; a typical state machine requires a large amount of written information and thus depends heavily on the programming language used to build the software application under design.

Limitations

UML state machines are not purely diagrammatical; a typical state machine requires a large amount of written information and thus depends heavily on the programming language used to build the software application under design.

Integrating UML Diagrams with other Diagram Techniques to Model Systems in Industrial

Engineering

Object-oriented languages such as UML can be used to model very complex software applications. However, UML emphasizes the preliminary phases of software development and is typically used to describe the ideal functionality of a system.

An increasing number of software developers are using UML and associated visual modeling tools as a basis for the design and implementation of their distributed component-based applications. UML models can be integrated with other models and with domain specific languages. This article discusses the techniques for using UML in systems integration projects. It discusses some of the design issues facing systems integrators and the reason for using UML as a design notation within the context of a simplified case study of a typical call-center environment.

Systems integrations is the practice of building end-to-end solutions comprising prebuilt

components integrated together to form a whole. Such systems usually comprise many components that are brought from various vendors and glued together using various software techniques. The focus of the project is to focus on leveraging as much as possible the package functionality and minimizing the coding content. An example of a systems integration project is the IT infrastructure of a new supermarket; EPOS terminals integrated with stock control systems and staff management systems provide a single coherent view of the activity within the store. In engineering, systems integration is the bringing together of component subsystems into one system and ensuring that the subsystems function together as a system. In information technology, systems integration is the process of linking together different computing systems and software applications, physically or functionally to act as a coordinated while.

Other existing diagramming techniques

Diagramming Principles

There are to principles that are common to all diagramming techniques. Each diagram should be able to present a view of the entire system independent of other views and must be clear and fully understood. The context of the diagram must be understood from the viewpoint of its title, title block, a reference to a larger (smaller) context, or some combination thereof (Teory, 1990).

1. Logic Flow Charts

Refer to Appendix 1

Flowcharts place their focus on decisions which is a special process that is used in data-flow and object diagrams. The shapes are used to create conventional flowcharts. The techniques used in flowcharts include:

1. Functions, or processes, are represented by rectangles.

2. Decisions represented by diamonds.

3. Inputs represented by parallelograms.

4. Outputs represented by a hardcopy symbol (a rectangle with a wavy bottom edge).

Nassi-Schneiderman Diagrams also referred to as Chapin Charts,

are a modern alternative to flowcharts. They can be drawn using text and lines showing processes by series, by selection or by iteration. They are read from top to bottom and are more structured than flowcharts

2. Entity Relationship Diagrams

Entity Relationship Diagrams are used to model the entities that a computer system records information about, and the relationships between those entities (Chen, 1976). They can be created from an existing database schema or they can be created from scratch. They begin with a user-readable form that allows validation of a design and progress into culminating in versions that are used by developers to validate a design (Chen, Peter, et. al., 1999).

3. Data Flow Diagrams

It is a formal, structured analysis approach that assists in the functional decomposition process. They are comprised of four components (Martin, James & O'Dell, 1998):

1. External interactors represented by a rectangle.

2. Data stores represented by an open rectangle (2 or 3 sides)

3. Processes represented by any rounded object (a circle, oval, or square with rounded corners).

4. Data flows represented by arrows, with labels indicating their content.

4. Object Oriented Diagrams

Object oriented diagrams made a great contribution to the development of UML (Martin, James & O'Dell, 1998). The Sally Shlaer and Stephen Mellor method is used on projects that have not adopted the UML. It major components are (Booch, 1994):

• Domain chart - used to partition the system into domains and subsystems.

• Information Model - used to build a static analysis model of a system, showing objects, relationships, and inheritance structures

• State model - used to analyze the object's behavior over time.

• Process Diagram, or Action Data Flow Diagram

• Object Communication Model (OCM) - summarizes

the asynchronous event communication between state models in the system.

• Object Access Model (OAM) - summarizes the synchronous communication between state models and object instance data.

James Rumbaugh proposed an alternative methodology on Object Oriented Diagrams. His model defines class, object, state, and data-flow diagrams to model a system analysis and design (Rumbaugh, Blaha, Premlani, Eddy & Lorensen,1991). Some of the attributes of the object models include the object diagram, state-transition diagram (dynamic model) and data flow diagram (functional model). The advantage of the object modeling technique is that it allows for two different models of data to be displayed in the same diagram. Therefore, one diagram can show two different levels of association.

Grady Booch notation is the most complete method for representing the object-oriented systems (Coleman, 1999). It is however very complex and can lead to duplication and fragmentation of information across model diagrams. His model is made up of six diagrams: class, object, state transition, interaction, module, and process.