System models Objectives Topics covered System modelling Model types

System models Objectives Topics covered System modelling Model types www.phwiki.com

System models Objectives Topics covered System modelling Model types

Butler, Michael, Morning On-Air Personality/Sports Director/News Director has reference to this Academic Journal, PHwiki organized this Journal System models Objectives To explain why the context of a system should be modelled as part of the RE process To describe behavioural modelling, data modelling in addition to object modelling To introduce some of the notations used in the Unified Modeling Language (UML) To show how CASE workbenches support system modelling Topics covered Context models Behavioural models Data models Object models CASE workbenches

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System modelling System modelling helps the analyst to underst in addition to the functionality of the system in addition to models are used to communicate with customers. Different models present the system from different perspectives External perspective showing the system’s context or environment; Behavioural perspective showing the behaviour of the system; Structural perspective showing the system or data architecture. Model types Data processing model showing how the data is processed at different stages. Composition model showing how entities are composed of other entities. Architectural model showing principal sub-systems. Classification model showing how entities have common characteristics. Stimulus/response model showing the system’s reaction to events. Context models Context models are used to illustrate the operational context of a system – they show what lies outside the system boundaries. Social in addition to organisational concerns may affect the decision on where to position system boundaries. Architectural models show the system in addition to its relationship with other systems.

The context of an ATM system Process models Process models show the overall process in addition to the processes that are supported by the system. Data flow models may be used to show the processes in addition to the flow of in as long as mation from one process to another. Equipment procurement process

Behavioural models Behavioural models are used to describe the overall behaviour of a system. Two types of behavioural model are: Data processing models that show how data is processed as it moves through the system; State machine models that show the systems response to events. These models show different perspectives so both of them are required to describe the system’s behaviour. Data-processing models Data flow diagrams (DFDs) may be used to model the system’s data processing. These show the processing steps as data flows through a system. DFDs are an intrinsic part of many analysis methods. Simple in addition to intuitive notation that customers can underst in addition to . Show end-to-end processing of data. Order processing DFD

Data flow diagrams DFDs model the system from a functional perspective. Tracking in addition to documenting how the data associated with a process is helpful to develop an overall underst in addition to ing of the system. Data flow diagrams may also be used in showing the data exchange between a system in addition to other systems in its environment. Insulin pump DFD State machine models These model the behaviour of the system in response to external in addition to internal events. They show the system’s responses to stimuli so are often used as long as modelling real-time systems. State machine models show system states as nodes in addition to events as arcs between these nodes. When an event occurs, the system moves from one state to another. Statecharts are an integral part of the UML in addition to are used to represent state machine models.

Statecharts Allow the decomposition of a model into sub-models (see following slide). A brief description of the actions is included following the ‘do’ in each state. Can be complemented by tables describing the states in addition to the stimuli. Microwave oven model Microwave oven state description

Microwave oven stimuli Microwave oven operation Semantic data models Used to describe the logical structure of data processed by the system. An entity-relation-attribute model sets out the entities in the system, the relationships between these entities in addition to the entity attributes Widely used in database design. Can readily be implemented using relational databases. No specific notation provided in the UML but objects in addition to associations can be used.

Library semantic model Data dictionaries Data dictionaries are lists of all of the names used in the system models. Descriptions of the entities, relationships in addition to attributes are also included. Advantages Support name management in addition to avoid duplication; Store of organisational knowledge linking analysis, design in addition to implementation; Many CASE workbenches support data dictionaries. Data dictionary entries

Butler, Michael WTLS-AM Morning On-Air Personality/Sports Director/News Director www.phwiki.com

Object models Object models describe the system in terms of object classes in addition to their associations. An object class is an abstraction over a set of objects with common attributes in addition to the services (operations) provided by each object. Various object models may be produced Inheritance models; Aggregation models; Interaction models. Object models Natural ways of reflecting the real-world entities manipulated by the system More abstract entities are more difficult to model using this approach Object class identification is recognised as a difficult process requiring a deep underst in addition to ing of the application domain Object classes reflecting domain entities are reusable across systems Inheritance models Organise the domain object classes into a hierarchy. Classes at the top of the hierarchy reflect the common features of all classes. Object classes inherit their attributes in addition to services from one or more super-classes. these may then be specialised as necessary. Class hierarchy design can be a difficult process if duplication in different branches is to be avoided.

Object models in addition to the UML The UML is a st in addition to ard representation devised by the developers of widely used object-oriented analysis in addition to design methods. It has become an effective st in addition to ard as long as object-oriented modelling. Notation Object classes are rectangles with the name at the top, attributes in the middle section in addition to operations in the bottom section; Relationships between object classes (known as associations) are shown as lines linking objects; Inheritance is referred to as generalisation in addition to is shown ‘upwards’ rather than ‘downwards’ in a hierarchy. Library class hierarchy User class hierarchy

Key points Semantic data models describe the logical structure of data which is imported to or exported by the systems. Object models describe logical system entities, their classification in addition to aggregation. Sequence models show the interactions between actors in addition to the system objects that they use. Structured methods provide a framework as long as developing system models.

Butler, Michael Morning On-Air Personality/Sports Director/News Director

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