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An example of two components expressed in UML 2.0. The checkout component, responsible for facilitating the customer's order, requires the card processing component to charge the customer's credit/debit card (functionality that the latter provides).
Programming paradigms |
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Component-based software engineering (CBSE), also called as components-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a given software system. It is a reuse-based approach to defining, implementing and composing loosely coupled independent components into systems. This practice aims to bring about an equally wide-ranging degree of benefits in both the short-term and the long-term for the software itself and for organizations that sponsor such software.
Software engineering practitioners regard components as part of the starting platform for service-orientation. Components play this role, for example, in web services, and more recently, in service-oriented architectures (SOA), whereby a component is converted by the web service into a service and subsequently inherits further characteristics beyond that of an ordinary component.
Components can produce or consume events and can be used for event-driven architectures (EDA).
Definition and characteristics of components[edit]
An individual software component is a software package, a web service, a web resource, or a module that encapsulates a set of related functions (or data).
All system processes are placed into separate components so that all of the data and functions inside each component are semantically related (just as with the contents of classes). Because of this principle, it is often said that components are modular and cohesive.
With regard to system-wide co-ordination, components communicate with each other via interfaces. When a component offers services to the rest of the system, it adopts a provided interface that specifies the services that other components can utilize, and how they can do so. This interface can be seen as a signature of the component - the client does not need to know about the inner workings of the component (implementation) in order to make use of it. This principle results in components referred to as encapsulated. The UML illustrations within this article represent provided interfaces by a lollipop-symbol attached to the outer edge of the component.
However, when a component needs to use another component in order to function, it adopts a used interface that specifies the services that it needs. In the UML illustrations in this article, used interfaces are represented by an open socket symbol attached to the outer edge of the component.
A simple example of several software components - pictured within a hypothetical holiday-reservation system represented in UML 2.0.
Another important attribute of components is that they are substitutable, so that a component can replace another (at design time or run-time), if the successor component meets the requirements of the initial component (expressed via the interfaces). Consequently, components can be replaced with either an updated version or an alternative without breaking the system in which the component operates.
As a rule of thumb for engineers substituting components, component B can immediately replace component A, if component B provides at least what component A provided and uses no more than what component A used.
Software components often take the form of objects (not classes) or collections of objects (from object-oriented programming), in some binary or textual form, adhering to some interface description language (IDL) so that the component may exist autonomously from other components in a computer. In other words, a component acts without changing its source code. Although, the behavior of the component's source code may change based on the application's extensibility, provided by its writer.
When a component is to be accessed or shared across execution contexts or network links, techniques such as serialization or marshalling are often employed to deliver the component to its destination.
Reusability is an important characteristic of a high-quality software component. Programmers should design and implement software components in such a way that many different programs can reuse them. Furthermore, component-based usability testing should be considered when software components directly interact with users.
It takes significant effort and awareness to write a software component that is effectively reusable. The component needs to be:
- fully documented
- thoroughly tested
- robust - with comprehensive input-validity checking
- able to pass back appropriate error messages or return codes
- designed with an awareness that it will be put to unforeseen uses
In the 1960s, programmers built scientific subroutine libraries that were reusable in a broad array of engineering and scientific applications. Though these subroutine libraries reused well-defined algorithms in an effective manner, they had a limited domain of application. Commercial sites routinely created application programs from reusable modules written in assembly language, COBOL, PL/1 and other second- and third-generation languages using both system and user application libraries.
As of 2010, modern reusable components encapsulate both data structures and the algorithms that are applied to the data structures. Component-based software engineering builds on prior theories of software objects, software architectures, software frameworks and software design patterns, and the extensive theory of object-oriented programming and the object-oriented design of all these. It claims that software components, like the idea of hardware components, used for example in telecommunications,[1] can ultimately be made interchangeable and reliable. On the other hand, it is argued that it is a mistake to focus on independent components rather than the framework (without which they would not exist).[2]
History[edit]
The idea that software should be componentized - built from prefabricated components - first became prominent with Douglas McIlroy's address at the NATO conference on software engineering in Garmisch, Germany, 1968, titled Mass Produced Software Components.[3] The conference set out to counter the so-called software crisis. McIlroy's subsequent inclusion of pipes and filters into the Unixoperating system was the first implementation of an infrastructure for this idea.
Brad Cox of Stepstone largely defined the modern concept of a software component.[4] He called them Software ICs and set out to create an infrastructure and market for these components by inventing the Objective-C programming language. (He summarizes this view in his book Object-Oriented Programming - An Evolutionary Approach 1986.)
The software components are used in two different contexts and two kinds: i) using components as parts to build a single executable, or ii) each executable is treated as a component in a distributed environment, where components collaborate with each other using internet or intranet communication protocols for IPC (Inter Process Communications). The above belongs to former kind, while the below belongs to later kind.
IBM led the path with their System Object Model (SOM) in the early 1990s. As a reaction, Microsoft paved the way for actual deployment of component software with Object linking and embedding (OLE) and Component Object Model (COM).[5] As of 2010 many successful software component models exist.
Architecture[edit]
Kotor 2 sonic imprint sensor. A computer running several software components is often called an application server. This combination of application servers and software components is usually called distributed computing. Typical real-world application of this is in, e.g., financial applications or business software.
Component Models[edit]
A component model is a definition of properties that components must satisfy, methods and mechanisms for the composition of components.[6]
During the last decades, researchers and practitioners have proposed several component models with different characteristics. A classification of the existing component models is given in.[6] Examples of component models are: Enterprise JavaBeans (EJB) model, Component Object Model (COM) model, .NET model, and Common Object Request Broker Architecture (CORBA) component Model.
Technologies[edit]
- Business object technologies
- Component-based software frameworks for specific domains
- Earth System Modeling Framework (ESMF)
- MASH IoT Platform for Asset Management[7]
- KOALA component model developed for software in consumer electronics[8][9]
- Software Communications Architecture (JTRS SCA)
- Component-oriented programming
- Bundles as defined by the OSGi Service Platform
- Component web platform for modular js, css, and other assets
- Component Object Model (OCX/ActiveX/COM) and DCOM from Microsoft
- TASCS - SciDAC Center for Technology for Advanced Scientific Component Software
- Enterprise JavaBeans from Sun Microsystems (now Oracle)
- Fractal component model from ObjectWeb
- MidCOM component framework for Midgard and PHP
- Oberon, Component Pascal, and BlackBox Component Builder
- rCOS method of component-based model driven design from UNU-IIST
- SOFA component system from ObjectWeb
- The
System.ComponentModel
namespace in Microsoft .NET - Unity developed by Unity Technologies
- Unreal Engine developed by Epic Games
- UNO from the OpenOffice.org office suite
- VCL and CLX from Borland and similar free LCL library.
- XPCOM from Mozilla Foundation
- Compound document technologies
- Active Documents in Oberon System and BlackBox Component Builder
- KParts, the KDE compound document technology
- Object linking and embedding (OLE)
- Distributed computing software components
- .NET Remoting from Microsoft
- 9P distributed protocol developed for Plan 9, and used by Inferno and other systems.
- CORBA and the CORBA Component Model from the Object Management Group
- D-Bus from the freedesktop.org organization
- DCOM and later versions of COM (and COM+) from Microsoft
- DSOM and SOM from IBM (now scrapped)
- Ice from ZeroC
- Java EE from Sun
- Kompics[10] from SICS
- Universal Network Objects (UNO) from OpenOffice.org
- Web services
- Zope from Zope Corporation
- AXCIOMA (the component framework for distributed, real-time, and embedded systems) by Remedy IT
- COHORTE the cross-platform runtime for executing and managing robust and reliable distributed Service-oriented Component-based applications, by isandlaTech
- Generic programming emphasizes separation of algorithms from data representation
- Interface description languages (IDLs)
- Open Service Interface Definitions (OSIDs)
- Part of both COM and CORBA
- SIDL - Scientific Interface Definition Language
- Part of the Babel Scientific Programming Language Interoperability System (SIDL and Babel are core technologies of the CCA and the SciDAC TASCS Center - see above.)
- SOAPIDL from World Wide Web Consortium (W3C)
- XML-RPC, the predecessor of SOAP
- Inversion of Control (IoC) and Plain Old C++/Java Object (POCO/POJO) component frameworks
- Pipes and filters
- Unix operating system
See also[edit]
- Service Component Architecture (SCA)
- Software Communications Architecture (JTRS SCA)
References[edit]
- ^Foukalas et al 'Protocol Reconfiguration Using Component-Based Design'
- ^Wallace, Bruce (May 19, 2010). 'A hole for every component, and every component in its hole'. Existential Programming.
There is no such thing as a Component
- ^McIlroy, Malcolm Douglas (January 1969). 'Mass produced software components'(PDF). Software Engineering: Report of a conference sponsored by the NATO Science Committee, Garmisch, Germany, 7-11 Oct. 1968. Scientific Affairs Division, NATO. p. 79.
- ^Rainer Niekamp. 'Software Component Architecture'(PDF). Gestión de Congresos - CIMNE/Institute for Scientific Computing, TU Braunschweig. p. 4. Retrieved 2011-07-29.
The modern concept of a software component largely defined by Brad Cox of Stepstone, => Objective-C programming language
- ^Raphael Gfeller (December 9, 2008). 'Upgrading of component-based application'. HSR - Hochschule für Technik Rapperswill. p. 4. Retrieved 2011-07-29.
1990, IBM invents their System Object Model. 1990, as a reaction, Microsoft released OLE 1.0 OLE custom controls (OCX)
- ^ ab I. Crnkovic, S. Sentilles, A. Vulgarakis and M. R. V. Chaudron, 'A Classification Framework for Software Component Models' in IEEE Transactions on Software Engineering, vol. 37, no. 5, pp. 593-615, Sept.-Oct. 2011, doi: 10.1109/TSE.2010.83.
- ^MASH defines assets as people, property and information and management as monitoring, control and configuration. Presented at the 2013 IEEE IoT conference in Mountain View MASH includes a full IDE, Android client and runtime. 'MASH YouTube channel'
- ^A component-oriented approach is an ideal way to handle the diversity of software in consumer electronics. The Koala model, used for embedded software in TV sets, allows late binding of reusable components with noadditional overhead. [1]
- ^Component model for embedded devices like TV developed by Philips based on paper by van Ommering, R.: Koala, a Component Model for Consumer Electronics Product Software [2]
- ^Arad, Cosmin (April 2013). Programming Model and Protocols for Reconfigurable Distributed Systems(PDF). Doctoral Dissertation. Stockholm, Sweden: KTH Royal Institute of Technology. ISBN978-91-7501-694-8.
Further reading[edit]
- Brad J. Cox, Andrew J. Novobilski (1991). Object-Oriented Programming: An Evolutionary Approach. 2nd ed. Addison-Wesley, Reading ISBN0-201-54834-8
- Bertrand Meyer (1997). Object-Oriented Software Construction. 2nd ed. Prentice Hall.
- George T. Heineman, William T. Councill (2001). Component-Based Software Engineering: Putting the Pieces Together. Addison-Wesley Professional, Reading 2001 ISBN0-201-70485-4
- Richard Veryard (2001). Component-based business : plug and play. London : Springer. ISBN1-85233-361-8
- Clemens Szyperski, Dominik Gruntz, Stephan Murer (2002). Component Software: Beyond Object-Oriented Programming. 2nd ed. ACM Press - Pearson Educational, London 2002 ISBN0-201-74572-0
External links[edit]
- Why Software Reuse has Failed and How to Make It Work for You by Douglas C. Schmidt
- What is the True essence and reality of CBD? (Evidence to show existing CBD paradigm is flawed)
- comprehensive list of Component Systems on SourceForge
- Brief Introduction to Real COP (Component Oriented Programming) by Using a small GUI application as an example
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Component-based_software_engineering&oldid=903012039'
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Visual Basic provides full support for object-oriented programming including encapsulation, inheritance, and polymorphism.
Encapsulation means that a group of related properties, methods, and other members are treated as a single unit or object.
Inheritance describes the ability to create new classes based on an existing class.
Polymorphism means that you can have multiple classes that can be used interchangeably, even though each class implements the same properties or methods in different ways.
This section describes the following concepts:
- Classes and objects
- Class members
- Access modifiers and access levels
- Inheritance
Classes and objects
The terms class and object are sometimes used interchangeably, but in fact, classes describe the type of objects, while objects are usable instances of classes. So, the act of creating an object is called instantiation. Using the blueprint analogy, a class is a blueprint, and an object is a building made from that blueprint.
To define a class:
Visual Basic also provides a light version of classes called structures that are useful when you need to create large array of objects and do not want to consume too much memory for that.
To define a structure:
For more information, see:
Class members
Each class can have different class members that include properties that describe class data, methods that define class behavior, and events that provide communication between different classes and objects.
Properties and fields
Fields and properties represent information that an object contains. Fields are like variables because they can be read or set directly.
To define a field:
Properties have get and set procedures, which provide more control on how values are set or returned.
Visual Basic allows you either to create a private field for storing the property value or use so-called auto-implemented properties that create this field automatically behind the scenes and provide the basic logic for the property procedures.
To define an auto-implemented property:
If you need to perform some additional operations for reading and writing the property value, define a field for storing the property value and provide the basic logic for storing and retrieving it:
Most properties have methods or procedures to both set and get the property value. However, you can create read-only or write-only properties to restrict them from being modified or read. In Visual Basic you can use
ReadOnly
and WriteOnly
keywords. However, auto-implemented properties cannot be read-only or write-only.For more information, see:
Methods
A method is an action that an object can perform.
Note
In Visual Basic, there are two ways to create a method: the
Sub
statement is used if the method does not return a value; the Function
statement is used if a method returns a value.To define a method of a class:
A class can have several implementations, or overloads, of the same method that differ in the number of parameters or parameter types.
To overload a method:
In most cases you declare a method within a class definition. However, Visual Basic also supports extension methods that allow you to add methods to an existing class outside the actual definition of the class.
For more information, see:
Constructors
Constructors are class methods that are executed automatically when an object of a given type is created. Constructors usually initialize the data members of the new object. A constructor can run only once when a class is created. Furthermore, the code in the constructor always runs before any other code in a class. However, you can create multiple constructor overloads in the same way as for any other method.
To define a constructor for a class:
For more information, see: Object Lifetime: How Objects Are Created and Destroyed.
Destructors
Destructors are used to destruct instances of classes. In the .NET Framework, the garbage collector automatically manages the allocation and release of memory for the managed objects in your application. However, you may still need destructors to clean up any unmanaged resources that your application creates. There can be only one destructor for a class.
For more information about destructors and garbage collection in the .NET Framework, see Garbage Collection.
Events
Events enable a class or object to notify other classes or objects when something of interest occurs. The class that sends (or raises) the event is called the publisher and the classes that receive (or handle) the event are called subscribers. For more information about events, how they are raised and handled, see Events.
- To declare events, use the Event Statement.English Skills With Readings PDF Download. Hallo readers!!! What you can after you read the English Skills With Readings PDF Download?You certainly get a lot of some things that have not been what you get.therefore I really like to read this book This English Skills With Readings PDF Kindle will add to a collection of the best books of the year. English skills with readings pdf free. English Skills with Readings Pdf mediafire.com, rapidgator.net, 4shared.com, uploading.com, uploaded.net Download; Note: If you're looking for a free download links of English Skills with Readings Pdf, epub, docx and torrent then this site is not for you. Ebookphp.com only do ebook promotions online and we does not distribute any free download.
- To raise events, use the RaiseEvent Statement.
- To specify event handlers using a declarative way, use the WithEvents statement and the Handles clause.
- To be able to dynamically add, remove, and change the event handler associated with an event, use the AddHandler Statement and RemoveHandler Statement together with the AddressOf Operator.
Nested classes
A class defined within another class is called nested. By default, the nested class is private.
To create an instance of the nested class, use the name of the container class followed by the dot and then followed by the name of the nested class:
Access modifiers and access levels
All classes and class members can specify what access level they provide to other classes by using access modifiers.
The following access modifiers are available:
Visual Basic Modifier | Definition |
---|---|
Public | The type or member can be accessed by any other code in the same assembly or another assembly that references it. |
Private | The type or member can only be accessed by code in the same class. |
Protected | The type or member can only be accessed by code in the same class or in a derived class. |
Friend | The type or member can be accessed by any code in the same assembly, but not from another assembly. |
Protected Friend | The type or member can be accessed by any code in the same assembly, or by any derived class in another assembly. |
For more information, see Access levels in Visual Basic.
Instantiating classes
To create an object, you need to instantiate a class, or create a class instance.
After instantiating a class, you can assign values to the instance's properties and fields and invoke class methods. Fallout 4 add caps console command.
To assign values to properties during the class instantiation process, use object initializers:
For more information, see:
Shared classes and members
A shared member of the class is a property, procedure, or field that is shared by all instances of a class.
To define a shared member:
To access the shared member, use the name of the class without creating an object of this class:
Shared modules in Visual Basic have shared members only and cannot be instantiated. Shared members also cannot access non-shared properties, fields or methods
For more information, see:
Anonymous types
Anonymous types enable you to create objects without writing a class definition for the data type. Instead, the compiler generates a class for you. The class has no usable name and contains the properties you specify in declaring the object.
To create an instance of an anonymous type:
For more information, see: Anonymous Types.
Inheritance
Inheritance enables you to create a new class that reuses, extends, and modifies the behavior that is defined in another class. The class whose members are inherited is called the base class, and the class that inherits those members is called the derived class. However, all classes in Visual Basic implicitly inherit from the Object class that supports .NET class hierarchy and provides low-level services to all classes.
Note
Visual Basic doesn't support multiple inheritance. That is, you can specify only one base class for a derived class.
To inherit from a base class:
By default all classes can be inherited. However, you can specify whether a class must not be used as a base class, or create a class that can be used as a base class only.
To specify that a class cannot be used as a base class:
To specify that a class can be used as a base class only and cannot be instantiated:
For more information, see:
Overriding members
By default, a derived class inherits all members from its base class. If you want to change the behavior of the inherited member, you need to override it. That is, you can define a new implementation of the method, property or event in the derived class.
The following modifiers are used to control how properties and methods are overridden:
Visual Basic Modifier | Definition |
---|---|
Overridable | Allows a class member to be overridden in a derived class. |
Overrides | Overrides a virtual (overridable) member defined in the base class. |
NotOverridable | Prevents a member from being overridden in an inheriting class. |
MustOverride | Requires that a class member to be overridden in the derived class. |
Shadows | Hides a member inherited from a base class |
Interfaces
Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes. An interface represents a contract, in that a class that implements an interface must implement every aspect of that interface exactly as it is defined.
To define an interface:
To implement an interface in a class:
Object Oriented Programming C++ In Hindi Pdf
For more information, see:
Generics
Classes, structures, interfaces and methods in .NET can include type parameters that define types of objects that they can store or use. The most common example of generics is a collection, where you can specify the type of objects to be stored in a collection.
To define a generic class:
To create an instance of a generic class:
For more information, see:
Delegates
A delegate is a type that defines a method signature, and can provide a reference to any method with a compatible signature. You can invoke (or call) the method through the delegate. Delegates are used to pass methods as arguments to other methods.
Note
Event handlers are nothing more than methods that are invoked through delegates. For more information about using delegates in event handling, see Events.
Object-oriented Programming Tutorial
To create a delegate:
To create a reference to a method that matches the signature specified by the delegate:
For more information, see: