HAS

Patterns The use of patterns is essentially the reuse of well established good ideas. A pattern is a named well understood good solution to a common problem in context. Patterns describe how objects communicate without become entangled in each other’s data models and methods. Keeping this separation has always been an objective of good OO programming, objects should mind their own business, but obviously need the services of other objects as well. Definition “Patterns identify and specify abstractions that are above the level of single classes and instances, or of components”. Patterns can exist at many levels from very low level specific solutions to broadly generalised system issues. Patterns are often described using UML together with a pattern template A template describes a pattern. Typical template may contain: Name, Intent, AKA, Motivation, Application, Structure, Participation, Collaborations, Consequences, Implementation, Sample Code, Known Uses, Related Patterns. Main advantages capture best practice, reuse, fairly standard way of describing patterns. Disadvantages: advanced topic, learning design patterns is a long multiple step process; Acceptance, Recognition, Internalisation, on the other hand they are worth learning. Role of experience. More geared to OO than other computing paradigms.

Patterns The use of patterns is essentially the reuse of well established good ideas. A pattern is a named well understood good solution to a common problem in context. Patterns describe how objects communicate without become entangled in each other’s data models and methods. Keeping this separation has always been an objective of good OO programming, objects should mind their own business, but obviously need the services of other objects as well. Definition “Patterns identify and specify abstractions that are above the level of single classes and instances, or of components”. Patterns can exist at many levels from very low level specific solutions to broadly generalised system issues Patterns are often described using UML together with a pattern template. A template describes a pattern. Typical template may contain: Name, Intent, AKA, Motivation, Application, Structure, Participation, Collaborations, Consequences, Implementation, Sample Code, Known Uses, Related Patterns. Main advantages capture best practice, reuse, fairly standard way of describing patterns Disadvantages: advanced topic, learning design patterns is a long multiple step process; Acceptance, Recognition, Internalisation, on the other hand they are worth learning. Role of experience. More geared to OO than other computing paradigms.

Action Languages ALs can create, delete, directly change (via assignment) and send state changing messages to objects. The action language is executable and allows us to describe and execute the actions an object performs when receiving a stimulus. AL features: Sequential Logic Access to the data described by the Class Diagram Access to the data supplied by signals initiating actions The ability to generate signals Access to timers Access to synchronous operations provided by classes and objects Access to operations provided by other MDA domains

Action Languages ALs can create, delete, directly change (via assignment) and send state changing messages to objects. The action language is executable and allows us to describe and execute the actions an object performs when receiving a stimulus. AL features: Sequential Logic Access to the data described by the Class Diagram Access to the data supplied by signals initiating actions The ability to generate signals Access to timers Access to synchronous operations provided by classes and objects Access to operations provided by other MDA domains

Action Languages OMG only define Action Language Semantics (ASL) (not syntax), hence many possible flavors. Unlike conventional languages, there is no concept of a “main” function or routine where execution starts. Rather, ASL is executed in the context of a number of interacting state machines, all of which are considered to be executing concurrently and in the context of synchronous call stacks invoked from these state machines or directly from outside the system. Any state machine, on receipt of a signal (from another state machine or from outside the system) may respond by changing state. On entry to the new state, a block of processing is performed. This processing can, in principle execute at the same time as processing associated with another state machine. In short ALs support concurrency and animate UML models, In particular statecharts and interaction diagrams can be run by: 1) creating objects with the keyword create 2) linking objects with the keyword link 3) sending messages with the keyword generate

Action Languages Role in development. Because ALs can create objects and send messages to objects, they permit a range of modelling, prototyping and testing tasks. ALs can be used during analysis and design to specify and test (or check) general purpose constraints and other modeling needs. MDA aspect. ASL (Action Specification Language ) is designed to fill the semantic gap in UML and conforms to the UML Action Semantics Request for Proposal issued by the OMG. It supports platform independently action specifications [PIMS] for UML models and provides easy-to-understand operations on UML classes, objects and associations (which is not the case in usual programming languages). Realtime ASL useful for real-time embedded system, with high concurrency and timers/triggers required. ASL can directly model behavior whereas OCL can only model constraints about behavior.