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Object-Oriented Frameworks

Object-Oriented Frameworks. Wei-tek Tsai Department of Computer Science and Engineering University of Minnesota Minneapolis MN,55455 tsai@cs.umn.edu. What will be covered. Issues in component based software development Concepts of the framework What is object-oriented framework

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Object-Oriented Frameworks

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  1. Object-Oriented Frameworks Wei-tek Tsai Department of Computer Science and Engineering University of Minnesota Minneapolis MN,55455 tsai@cs.umn.edu

  2. What will be covered • Issues in component based software development • Concepts of the framework • What is object-oriented framework • What have been provided by the framework • Framework Introduction • IBM San Francisco Framework • Using the IBM SF framework • IBM SF techniques • Enterprise Java Beans Specification • Microsoft COM+ Idea • Framework based software engineering

  3. Issues in the Object-Oriented Software Development • Software reuse • Software reuse is difficult, especially • in large scale (enterprise level) • cross business domain • cross software platform • cross hardware platform • Most people reuse their own code, rely on themselves

  4. Component based software development • Several Component model have been proposed to address software reuse and distributed objects management issues. Which helps to achieve the cross hardware and cross software platform software reuse. • Component model is essentially based on the common interfaces defined at the class/method level. • Java Bean • CORBA • COM/DCOM ActiveX • The “languages” for the object world.

  5. Issues in Component based software development • Can component model solve the software reuse issues? • Currently off the shelf component reuse is almost impossible • you just can not find the component you want. • you just can not find a proper shelf to put your component on it. • Where to put/find? • How to put/find? • Which one to choose? • Why choose • Although component has the facilities to talk to each other, they talk on different topics in different way.

  6. Issues in Component based software development (cont.) • To make components cooperate with other components(reusable), there are two approaches • Make them smart enough, so that they can understand everything. Agent/Real Person? • To construct them into standard shape, so that they understand something. • when different components talking on the same topic, they should talk in the same way. • build a standard host of components = define the shapes of the components = build the shelf for components • different vendors’ components on the same position of the shelf can be reused by anybody who need the component on that position

  7. Which approach is practical? • To construct component into standard shape, so that they understand something. • Build the Shelf for the component, so that • you know where should put the your component • I know where I can find the component I want • Limitations for this approach • To make your component can be reused by other people, you can not design your component freely. Commit to certain shape is essential. • To share components belong to different shelves is difficult

  8. What is a good shelf for components? • Criteria for a good shelf • Based on the standard component model • Support different hardware/software platforms • Clear decomposition of the application domain • Component should be reusable • Component should be extensible • Open standard • ...

  9. What is object-oriented framework? • OO framework is a set of cooperating classes that make up a reusable design for a specific class of software. • OO framework is partially finished OO application. Application developers can extend framework to modify/add/remove existing functions provided by the framework. • OO framework is the shelf for software components.

  10. What should be provided by a framework • As a partially finished application, the following points are essential which should be provided by any framework • Architecture • Layered architecture / Multi-tier architecture • Object-bus • CORBA/COM/Java Bean/Others.. • Functionality • Based on Common requirement / Business requirement • Extension rules • How to extend the framework • It may also provide the following • Developing tools/Programming guide/Testing support …

  11. Framework Categories (Decomposed by functionality) • Horizontal Framework • Provides common services for multiple application domains. (distributed object management, transaction service and persistent service etc.) • Example: • The base layer of the IBM SF framework • WebObjects • CORBA, ActiveX/COM/DCOM (Distributed object management) • Vertical Framework • Provided for a specific application domain, contain more domain knowledge. (banking, insurance and manufacturing etc.) • Example: • The General Ledger provided by the IBM SF framework

  12. Class Library static, use only Include Design Code No application flow Can not be treat as an application Framework dynamic, can be extended Include architecture process design/code Application flow A mini application Framework vs. Class Library

  13. How to use the framework • Use the services provided by the framework • Extend the functions provided by the framework • Application developers should expect change in all the stages in the software development process (requirement, design, implementation, testing and maintain).

  14. What is the IBM San Francisco Framework • IBM SF Framework is a sharable framework. • Defines a common architecture for applications in different domains. • It allows different vendors to build their own component for the framework. • Component developed by different vendors can be reused by other people using the IBM SF framework • A combination of horizontal and vertical frameworks.

  15. Goals of the IBM SF Framework (I) • Flexible application business frameworks that reduce the complexity, expense, and time-to-market for software vendors to build customized multi-platform systems. • Using San Francisco, software vendors can produce robust solutions built on top of high-level reusable business frameworks that are internet-enabled, scaleable and multi-platform client/server.

  16. Goals of the IBM SF framework(II) To help application developers by: • Offering a common foundation for developing business applications. • Achieve large scale, cross platform, cross domain software reuse • Providing a cost-effective way to add the capabilities that customers demand • Allowing them to focus development resources to make their products unique

  17. A close look at the IBM SF framework (I) • Architecture - Layered Architecture • Three major layers. • Foundation Layer (Base Layer) • Common Business Objects • Common Business Processes • Object Bus - Private bus • Has its own object bus implementation • Not followed the common object bus standard, but similar to CORBA.

  18. A close look at the IBM SF framework (II) • Functionality • Base Layer is a horizontal framework which provides the common services for different application domains. • Naming Service • Distributed Object Management Service • Persistent Service • Transaction Service • Common Business Processes layer provides domain specific functionality. Contains business requirement for banking domain. • General Legal

  19. A close look at the IBM SF Framework (III) • Extension Rules • Design patterns are widely adopted to help application developers to use and extend the framework. • Extension points are clearly specified through out the entire framework for application developers to extend the framework.

  20. A close look at the IBM SF framework (IV) • Defines its own programming modals/rules based the Java language • For example: • Class name with “impl” means the class represents a distributed object • Dependent subclass’s name begin with a “D”, such as Dtime. • Provides code generator for application developers

  21. Architecture of the IBM SF Framework

  22. The Base Layer (Fundamental Layer) • The lowest level of the framework • It provides • Foundation Object Model Classes • Entity/ Dependant / Command ... • Kernel Services • Distributed Object Management • Naming Service • Transaction Service • Persistent Service • Utilities

  23. Foundation Object Model • Class Hierarchy of several major classes of the Base Layer • All these are interfaces defined in the Base Layer Object Base BusinessObject BaseFactory Entity Dependant DynamicEntity Command

  24. Entity Object • The independent, sharable, objects that are used in the operation of the business. • Often associated with data, it is the core to an application or framework • Persistent Objects, associated with an underlying persistent storage mechanism. • Example of Entity Object • Person, Account, Order • Example of Non-Entity Object • String • PrintMg (an object provides printing service)

  25. BaseImpl destroy() equals(Object) externalizeToStream() initialize() internalizeFromStream() isIdentical() toString() uninitialize() Entity isDirty() getHandle() notifyObserver() update() Entity Class Hierarchy Base extends extends EntityImpl Implements

  26. Dependant Object • A dependant object is a lightweight business objects that encapsulate a small amount of data, usually it is not required to be saved in persistent storage • If the dependant object is contained in an Entity, the dependent object will be saved in the persistent storage • Transient Dependent objects can stand alone • Example of Dependent • DTime • Command

  27. Command Object • A specialized type of Dependent object. • Commands represent business tasks, calculations, and other actions that control or modify Entities. • Support logging , redo and undo. • Commands can be used to perform their task atomically or as part of a larger transaction. • Commands can be created to execute their task in a remote server process or locally. • Commands are often transient but may be persistent if contained in an Entity.

  28. Kernel ServicesDistributed Object Management (I) • Provide platform independent distributed object management services, similar to OMG CORBA architecture • Clients Function support: • Create instances of distributed objects • Refer to an existing persistent object • Create new objects • Invoke methods on distributed objects • Transparency • Exchange complex parameters

  29. Kernel ServicesDistributed Object Management (II) • Naming Services • Objects can be uniquely identified in the network • Provide installation utility, similar to the registration process in the CORBA architecture • Locking and commitment control • Part of the locking mechanisms of CORBA are supported (only optimistic locking) • Java Remote Method Invocation(RMI) is the major communication infrastructure used in IBM SF framework

  30. Kernel ServicesTransaction Services • Most business objects in the San Francisco frameworks represent shared, persistent data and operations • Entities can only been accessed as a part of a transaction • The scope of a transaction is defined by using the following commands: • begin : Identify the beginning of a transaction • commit : Identify the successful completion of a transaction • rollback : Identify the unsuccessful completion of a transaction • rollbackOnly : Notify that the current transaction can not be commit. • getTransactionStatus: return the current status of the transaction

  31. Kernel ServicesPersistent Services • Standard interface defined in the object Base • internalizeFromStream(BaseStream) • externalizeToStream(BaseStream) • Application developers should implement these in their own Entity to save/retrieve data to/from persistent storage • From the application developer’s point of view, there is no difference whether the data is saved in a database of file system. • Using configuration tools to configure the object container, either using odbc(save in database) or posix(save in files).

  32. BaseFactory Interface • BaseFactory is the central interface to application developer of all the kernal services provided by the base layer • Manages creating, deleting, and accessing all business objects in a distributed environment. • Manages transactions, distribution connections, persistence, and security checks as objects are accessed.

  33. TransactionManagement begin() commit() getTransactionStatus() rollback() rollbackOnly() DependantManagement CommandManagement copyDependant() createDependant() deleteDependant() executeCommand() redoExecuteCommand() undoExecuteCommand() EntityManagement getEntity() deleteEntity() createEntity() dropAccess() syncEntity() Base Factory Class Diagram Other interface.. BaseFactory

  34. Common Business Objects • The middle layer of the IBM SF framework • Object uses the services provided by the Base Layer. • Most of the Common Business Objects are a concrete Entity, Dependant or Command. • Common Business Object are general objects which can be reused in different business domains • Examples of CBO: • Address • Company • BusinessPartner • CheckingAccount

  35. Common Business Processes • The top layer of the IBM SF Framework • Contains business requirement • Build on top of the Common Business Objects layer, provides application flow and behaviors. • A vertical framework with extension points, can be extended to build similar applications • Represents the highest level of software reuse • Examples of CBP: • The General Legal provided by the IBM SF framework

  36. IBM SF Framework (Background Information) • 1.0 Beta Released August 15th, 1997 • Java 270KLOC, C++ 15KLOC • 3000 Downloads • A complex object-oriented application, contains over thousand of classes. • 1.2 will be available in March 1998 at Java One. • 3 times faster than the current version

  37. Building the IBM SF Framework(Background Information) • Around 150 people involved in developing the IBM SF framework • Skills used to build the IBM SF Framework • 40% Domain experts (based in European) • 40% OO programmers • 10% Application developers (above CBO) • 10% Highly skilled OO designers/architectures

  38. Using the IBM SF Framework • Use the framework at the Base Layer as a horizontal framework • Use general services • Use the framework at the CBO layer • Use generic business objects • Use the framework as the specialized Business Process • Application structure and behaviors of a special business process • Use the vertical part • Tradeoff between reusability and generality • The more reusable, the more general

  39. How to Use the Services provided by the IBM SF Framework • Understand the IBM SF architecture • Know the what services have been provided by the IBM SF Framework • Understand how the services are provided to the applications using the framework • Example: • How the Common Business Objects use the services provide by the base layer.

  40. Layer Interactions Between the CBO and the Base Layer(I) • Common Business Object are constructed based on the base layer • CBO can be shared by different applications since they are constructed based on the same layer. • The base layer provides its service to the upper layer in the following ways: • Conceptual interface (Foundation Objection model) • Application developer should inherit from the conceptual interface in order to get the services provided by the base layer • Direct method invocation • Similar to the class library

  41. Entity Dependent Command Layer Interactions Between the CBO and the Base Layer(II) Domain Application Domain application Common object1 object2 Object 3 Persistent Management Distributed Services (Naming Services, Remote Method Invocation,) Transaction Service Security services

  42. Using the Persistent Service (I) • When you should consider to create a persistent object • The object can be shared by multiple users simultaneously at the run time • The object should be saved while the application is not running (At the creation time, theobject is associated with a form of permanent storage such as file system or data base.) • Persistent objects • Account • User • Not persistent objects • PrintMg (an object provides printing service)

  43. Using the Persistent Service (II) • How persistent service is provided in the IBM SF framework • Entity is an interface defined by IBM SF framework to provide persistent service • Object should inherit from the Entity/EntiryImpl to get the persistent services(Stored in the persistent storage). • Factory design pattern is used to create new “Entities”.

  44. Using the Persistent Service (III) • The Class Diagram and Methods of the Entity Method Implementation Property definition Method Definition implements Entity EntityImpl • initialize • externalizeToStream • internalizeFromStream • toString • ... • initialize {} • externalizeToStream {} • internalizeFromStream {} • toString {} • ...

  45. Using the Persistent Service (IV) Entity EntityImpl implments extends extends CheckBookFactory • createCheckBook CheckBook CheckBookImpl implments

  46. Using the Persistent Service (V) CheckBook Name Address Balance CreditLimit Password getName/setName getAddress/setAddress getBalance/setBalance getCreditLimit/setCreditLimit getPassword/setPassword EntityImpl CheckBookImpl Property definitions Method implementations Override methods defined in EntityImpl externalizeToStream(), initialize(), internalizeFromStream(), toString. Entity CheckBookFactory CheckBook createCheckBook Method definitions

  47. Using the Persistent Service (VI) Global.factory().begin(); // transaction begin checkBookInst = CheckBookFactory.createCheckBook(…); // BaseFactory.createEntity() is called in this method. The framework // will create a new instant of the CheckBook entity . checkBookInst.setBalance(1000.00); // set property checkBookInst.setName(“Hello”); // set property .. Global.factory().commit(); //transaction commit // the externalizeToStream() will be called to output the data to the // persistent storage. • Here also the transaction service is used by using direct method call.

  48. What is affected if I use the base services (IBM SF)? • Object Creating, Deleting, Copying, Accessing, Updating • you never can use new() to create a new instance of class in SF. • Entity is a persistent object, new entity should be created within a transaction and must be committed to make sure it is save in the persistent store. • If you don’t use the base services? • You can’t use the entire framework at all.

  49. Extending the IBM SF Framework(I) • Extends based on the framework only • Extends the framework at the CBO layer • Create a new Common Business Object for your own application • Extends based on the applications using the framework • Change the CBO provided by other applications • Replace the CBO provided by other applications

  50. Extending the IBM SF Framework(II) • Find out the extension points specified by the framework designers • IBM SF framework specified the extension points in the framework • Design Patterns are used in the implementation of the extension points • Follow the extension mechanisms have been provided by the framework • Different extension mechanisms are provided for different kinds of extensions.

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