INTRODCUTION - University of Texas at Arlington

INTRODCUTION - University of Texas at Arlington

System Modelling System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers. Different models present the system from different perspectives External perspective showing the systems context or environment; Behavioural perspective showing the behaviour of the system; Structural perspective showing the system or data architecture. Model types 1. Context Model

2. Behavioural Models 3. 4. External View Illustrates Boundaries Component Based Data Flow Models State Machine Models Semantic Data Models Object Models Context models Context

models are used to illustrate the operational context of a system - they show what lies outside the system boundaries. Social and organisational concerns may affect the decision on where to position system boundaries. Architectural models show the system and its relationship with other systems. The context of an ATM system Security system Branch accounting system Account database Auto-teller system Branch counter

system Usage database Maintenance system 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 systems behaviour. Data-processing models Data flow diagrams (DFDs) may be used to model the systems data processing. These show the processing steps as data flows through a system. DFDs are an intrinsic part of many analysis methods. Simple and intuitive notation that customers can understand. Show end-to-end processing of data. Insulin pump DFD Blood Blood parameters Blood sugar sensor

Blood sugar analysis Blood sugar level Insulin requirement computation Insulin Pump control commands Insulin pump Insulin delivery controller Insulin requirement State machine models

These model the behaviour of the system in response to external and internal events. They show the systems responses to stimuli so are often used for modelling real-time systems. State machine models show system states as nodes and 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 and are used to represent state machine models. Microwave oven model Full power Full power do: set power

= 600 Timer Waiting do: display time Half power Number Full power Half power Set time Operation do: get number exit: set time do: operate

oven Door closed Timer Door open Half power do: set power = 300 Door closed Disabled do: display 'Waiting' Cancel Start Enabled do: display

'Ready' Door open Waiting do: display time Microwave oven state description State Description Waiting The oven is waiting for input. The display shows the current time. Half power The oven power is set to 300 watts. The display shows Half power. Full power

The oven power is set to 600 watts. The display shows Full power. Set time The cooking time is s et to the users input value. The display shows the cooking time selected and is updated as the time is set. Disabled Oven operation is disabled for safety. Interior oven light is on. Display shows Not ready. Enabled Oven operation is enabled. Interior oven light is off. Display shows Ready to cook. Operation Oven in operation. Interior oven light is on. Display shows the timer countdown. On completion of cooking, the buzzer is sounded for 5 s econds. Oven light is on. Display shows Cooking complete while buzzer is sounding. Microwave oven stimuli

Microwave oven operation Operation Checking do: check status Turntable fault OK Time Cook do: run generator Emitter fault Alarm do: display event Timeout

Done do: buzzer on for 5 secs. Door open Disabled Cancel Waiting 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 and the entity attributes

Widely used in database design. Can readily be implemented using relational databases. No specific notation provided in the UML but objects and associations can be used. Library semantic model Article title authors pdf file fee m published-in Source n fee-payable-to 1 1

delivers 1 in 1 1 n Order order number total payment date tax status n places 1 Buyer name address e-mail billing info Copyright

Agency 1 name has-links address title publisher issue date pages Country in 1 copyright form tax rate Data dictionaries

Data dictionaries are lists of all of the names used in the system models. Descriptions of the entities, relationships and attributes are also included. Advantages Support name management and avoid duplication; Store of organisational knowledge linking analysis, design and implementation; Many CASE workbenches support data dictionaries. Data dictionary entries 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 understanding of the application domain Object classes reflecting domain entities are reusable across systems Object models and the UML The UML is a standard representation devised by the developers of widely used object-oriented analysis and design methods. It has become an effective standard for object-oriented modelling. Notation Object classes are rectangles with the name at the top, attributes in

the middle section and operations in the bottom section; Relationships between object classes (known as associations) are shown as lines linking objects; Inheritance is referred to as generalisation and is shown upwards rather than downwards in a hierarchy. Library class hierarchy Library item Catalogue number Acquisition da te Cost Type Status Number ofcopies Acquire () Catalogue () Dispose () Issue () Return () Published item Recorded item

Title Medium Title Publisher Book Author Edition Publication date ISBN Magazine Year Issue Film Director Date of release Distributor Computer program Version

Platform User class hierarchy Library user Name Address Phone Registration # Register () De-register () Reader Borrower Items on loan Max. loans Affiliation Staff Department Department phone Student

Major subject Home address Multiple inheritance Rather than inheriting the attributes and services from a single parent class, a system which supports multiple inheritance allows object classes to inherit from several super-classes. This can lead to semantic conflicts where attributes/services with the same name in different super-classes have different semantics. Multiple inheritance makes class hierarchy reorganisation more complex. Multiple inheritance Book Voice recording

Author Edition Publication date ISBN Speaker Duration Recording da te Talking book # a Tpes Object aggregation An aggregation model shows how classes that are collections are composed of other classes. Aggregation models are similar to the part-of relationship in semantic data models. Object aggregation

Study pack Course title Number Year Instructor Assignment Credits Exercises #Problems Description OHP slides Slides Solutions Text Diagrams Lecture notes Text

Videotape Tape ids. Object behaviour modelling A behavioural model shows the interactions between objects to produce some particular system behaviour that is specified as a usecase. Sequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects. Issue of electronic items Ecat: Catalog :Library Item Lib1: NetServer :Library User

Lookup Display Issue Issue licence Accept licence Compress Deliver CASE workbenches A coherent set of tools that is designed to support related software process activities such as analysis, design or testing. Analysis and design workbenches support system modelling during both requirements engineering and system design. These workbenches may support a specific design method or may provide support for a creating several different types of system model. An analysis and design workbench

Data dictionary Structur ed diagramming tools Report generation facilities Code generator Central information repository Query langua ge facilities

Forms creation tools Design, anal ysis and checking tools Import/export facilities

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