Software architecture quiz 10

Contract

A lawful agreement between two parties in which both parties accept obligations and on which both parties can found their rights

Behavioral patterns

Allow a choice between alogirthms and the assignment responsibilites to objects, characterize complex control flows that are difficult to follow at runtime

Adapter pattern(wrapper)

Connects incompatible components Converts the interface of one component into another interface expected by the other (calling) component used to provide a new interface to existing legacy components(Interface engineering, reengineering_

Invariant

Contract constraint: a predicate that is always true for all instances of a class

Preconditions('rights')

Contract constraint: must be true before an operation is invoked

Contracts and formal specification

Contracts enable the caller and the provider to share the same assumptions about the class contract is an exact specification of the interface of an object

Object design

Decide where to put these operations in the object model, the process of adding details to the requirements analysis and making implementation decisions, serves as the basis of implementation

Object oriented contract

Describes the services that are provided by an object if certain conditions are fulfilled,specifies conditons under which the service will be provided, a specification of the result of the service

Strategy pattern

Different algorithms exist for a specific task and we can switch between algorithms at runtime as we need them, if needed, we can add a new algorithm without disturbing the application or the other alogirthms

Facade

Given a simulation of a mouse a maze, enable the path evaluation component to evaluate different paths independently of the types of moves considered by the mouse.

Do not apply an operation to the result of another operation

Information hiding design principles: Write a new operation that combines the two operations

Only the operations of a class are allowed to manipulate its attributes

Information hiding design principles: Access attributes only via operation

Hide external objects at subsystem boundary

Information hiding design principles: Define abstract class interfaces which mediate between the external world and the system as well as between subsystems.

Trade-off: Information hiding v. efficiency

Information hiding heuristics: Accessing a private attribute might be too slow

Always apply the 'need to know principle'

Information hiding heuristics: only if somebody needs to access the information, make it publicly possible, provide only well defined channels so you always know the access

The fewer details a class user has to know

Information hiding heuristics: The easier the class can be changed and the less likely they will be affected by any changes in the class implementation

Reuse

Object design activity 1 The identification of existing solutions with use of inheritance, off the shelf components and additional solution objects, use of design patterns

Interface specification

Object design activity 2 Describes precisely each class interface

Object model restructuring

Object design activity 3 Transforms the object design model to improve its understandability and extensability

Object model optimization

Object design activity 4 Transforms the object design model to address performance criteria such as response time or memory utilization

Bridge pattern

Provides a bridge between the abstraction in the application domain and the implementor in the solution domain, can be used to provide multiple implementations under the same interface, allows to postpone design decisions to the startup time of a system

Facade pattern

Provides a unified interface to a set of classes in a subsystem, consists of a set of public operations, each public operation is delegated to one or more operations in the classes behind the facade, defines a higher level interface that makes the subsystem easier to use, abstracts the details out

Structural patterns

Reduce coupling between two or more classes, introduce an abstract classes to enable future extension, encapsulate complex structures

adapter pattern used for

Should be used to interface existing components and legacy systems

Requirements analysis

The functional model and the dynamic model deliver operations for the object model

Formal specification

a contract in which invariants, rights and obligations in the contract are unambiguous

algorithm

a method for solving a problem using a finite sequence of well-defined instructions for solving a problem

Creational Patterns

allow to abstract from complex instatiation processes, make the system independent from the way its objects are created, composed, and represented

Abstract factory pattern

applicable for situations when independence from initialization or representation, manufacturer independence, constraints on related products, coper with upcoming change

Postcondition('obligation')

contract constraint: must be true after and operation is invoked

Pattern

describes a problem which occurs over and over again in our environment and then describes the core of the solution to that problem in such a way that you can use this solution a million times over without ever doing it the same way twice

Strategy

given a chess program, enable a monitoring component to switch planning algorithms at runtime based on the opposing player's style and response time.

Bridge

given a chess program, enable future developers to substitutes the planning algorithm that decides on the next move with a better one.

Adapter pattern

given a legacy banking application, encapsulate the existing business logic component

Carefully define the public interface for classes as well as subsystems

information hiding heuristics: For subsystems use a facade pattern if possible

Class implementor

private visibility, private attributes and operations can be accessed only by the class in which they are defined, they cannot be accessed by subclasses or other classes

Class extender

protected visibility, protected attributes/operations can be accessed by the class in which they are defined and by any descendant of the class

Class user

public visibility, public attributes/operation can be accessed by any class

Facade pattern used for

should be offered by all subsystems in a software system which provide a set of services. It delegates requests to the appropriate components within the subsystem, usually does not have to be changed when the components are changed

bridge pattern used for

should be used to interface to a set of objects with a large probability of change, when the full set of objects is not completely known at analysis or design time or when there is a chance that a subsystem or component must be replaced later after the system has been deployed and client programs use it in the field