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Patterns inSoftware EngineeringSoftware Engineering Lecturer: Raman RamsinLecturer:

Raman Ramsin

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Lecture 1 Earlier Patterns

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Patterns in Software Engineering – Lecture 1 Software Patterns „ Software Patterns support reuse of software architecture

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and design.

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Patterns capture the static and dynamic structures and

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Patterns capture the static and dynamic structures andcollaborations of successful solutions to problems that arisewhen building applications in a particular domain.

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Patterns represent solutions to problems that arise whendeveloping software within a particular contextdeveloping software within a particular context.

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i.e., “Pattern == problem/solution pair in a context”

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Patterns in Software Engineering – Lecture 1 Software Design Patterns „ “A

design pattern names, abstracts, and identifies the

key aspects of a common design structure that make ituseful for creating a reusable object-oriented design.”

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Design Patterns capture the static and dynamic structureand collaboration among key participants in softwaredesigns.

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They are particularly useful for articulating how and why toresolve non-functional forcesresolve non-functional forces.

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Patterns facilitate reuse of successful software architecturesand designs.

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Patterns in Software Engineering – Lecture 1 Coad's OO Patterns „ Seven basic Patterns:

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Item Description 2

Time Association

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Time Association

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Event Logging

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Roles Played

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State over a Collection

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Behavior over a Collection 7

Broadcast

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Patterns in Software Engineering – Lecture 1 Item Description

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Patterns in Software Engineering – Lecture 1 Pattern 2: Time Association „ If one needs to express attributes or services regarding anassociation between two objects, then an object from "time

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association" is needed. „^ A "time association" object often sends messages to itsparticipating objects to get values or get a sub-calculationparticipating objects to get values or get a sub calculationdone on its behalf. „^

Note that the association connection:^

captures the association for future queries about these objects. captures (for the sender) "to whom to send a message." „^ Use this pattern whenever the system is responsible to knowan association between two or more objects and to know ordo something about that association

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something about that association.

Patterns in Software Engineering – Lecture 1 Pattern 3: Event Logging „ A "device" object monitors an external device; the object

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is responsible for detecting that an event has occurred;

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is responsible for detecting that an event has occurred;

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is responsible for initiating a response to the event. P^

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„^ Part of the response may be to log the event's occurrence; when thisis the case, a "device" object sends the message "create" to the"event remembered" class to create an object with historical values. „^ A "device" object may know about some number of "eventremembered" objects; an "event remembered" object must knowabout a corresponding "device" object. „^ Use whenever an event is detected, and you need to log itsoccurrence to support after-the-fact analysis or to meet legaleq i ements

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requirements.

Patterns in Software Engineering – Lecture 1 Event Logging

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Patterns in Software Engineering – Lecture 1 Roles Played

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Patterns in Software Engineering – Lecture 1 Pattern 5: State over a Collection „ A "collection" object knows its state; this state applies to thecollection and may also apply to its parts, and each "member"

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object has its own state, too. „^ Use this pattern whenever there is whole-part in a businessdomain or implementation domain, and one or more attributesapply to the whole (the collection)apply to the whole (the collection).

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Patterns in Software Engineering – Lecture 1 Pattern 6: Behavior over a Collection „ A "collection" object has behavior that applies across an entire

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collection of its "member" objects. „^ Each "member" object performs actions, knowing (by means

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of its attributes) how to perform, without needed coordinationwith other "member" objects. „^ Use this pattern whenever there is whole-part in a domain,and a behavior (i.e., one or more services) applies across thewhole collection. „^ Caution: make the member objects do as much as they canwith what they know; only put behavior that really appliesacross the collection up in the "collection" object.

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Patterns in Software Engineering – Lecture 1 Behavior over a Collection

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Patterns in Software Engineering – Lecture 1 Broadcast

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Patterns in Software Engineering – Lecture 1 Coad Patterns: Example Model

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