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COM vs. CORBA

COM vs. CORBA. What are They?. COM: The Component Object Model is a software architecture that allows programs to be built from parts from different software producers.

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COM vs. CORBA

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  1. COM vs. CORBA

  2. What are They? • COM: The Component Object Model is a software architecture that allows programs to be built from parts from different software producers. • CORBA: The Common Object Request Broker Architecture is an open distributed object computing infrastructure that is being standardized by the Object Management Group (OMG).

  3. COM • Designed by Microsoft in 1993 • Primarily used with Windows • It is being replaced with Microsoft .NET although it can be used with .NET

  4. COM • COM provides the framework for interoperability and reusability of distributed objects. • Programmers can use different components from different vendors that communicate through COM. • Makes maintaining systems easier.

  5. COM • The main technologies that operate on the COM system are OLE, ActiveX, and MTS. • OLE aspects include compound documents, custom controls, inter-application scripting, data transfer, etc. • ActiveX allows programs to be web based. • MTS provides advanced features to allow COM to be used in enterprise solutions.

  6. COM

  7. What does COM do? • Defines a binary standard for component interoperability • Is Language-independent • Can support multiple platforms • Allows for component systems to grow • Is extensible

  8. What does COM do? • Communications between components, even across process and networks. (dcom) • Shared memory management between components • Error and status reporting • Dynamic loading of components

  9. How does COM do it? • The Binary structure • If the compiler can reduce language structures down to the specified binary representation. • This allows the communication at the binary level

  10. Vtables • COM defines a standard way to lay out virtual function tables in memory and a standard way to call functions through vtables. • Through this any language that can call functions through pointers can be used with COM. • This allows the sharing of resources by using multiples of an object, therefore reducing the memory requirement.

  11. Vtable

  12. COM Interfaces • An interface is not a class, it is just a group of related functions and is how components communicate. • Clients can only use interface pointers which abstract all functions. The only way an interface can be used is if it has a pointer. • A component usually has more than one interface because it has multiple services. • Interfaces never change, to make sure that all version can work together. If a new components is added it requires a new interface

  13. COM interface benefits • The functionality in applications to grow over time • All COM objects support QueryInterface which allows the making of more interfaces without changing the binary compatibility with existing code. • This also helps guarantees backward compatibility because of unchangeable interfaces.

  14. COM Interface benefits • Fast interaction because the calls are simply two memory pointers. The difference between a COM call and direct function call is negligible. • It allows for fast negotiation of interfaces because it is done in groups.

  15. COM Interface benefits • Interface reusability allows for code to be reused easily and makes it easy for programmers to remember a specific interface. • Allows for multiple higher level languages to be used. It breaks down the languages into a binary standard.

  16. COM Interface benefits • COM handles all calls to remote processes including network calls. COM will make the remote procedure call so that no additional code is required to make a remote function call. This functionality was added with the release of DCOM.

  17. COM Interface Benefits • COM creates a unique identifier that is a 128-bit integer so that there will be a way to correctly identify a component across a network of millions of components.

  18. COM Client/Server Model • The interaction between components creates a Client/Server model • The code that requests a function from a component is considered the client and the component that provides the function is considered the server. • This allows for a crash at the server level but will keep the client operating. • Clients can also represent themselves and act as a peer to peer service.

  19. COM Client/Server Model • There are 3 different types of servers • “in-process” means that the requested information is in the same process • “local” means that the location of the component is running on the same machine but in a different process • “remote” means that the component is on a different machine on the network.

  20. COM: IUnknown • IUnkown is a special interface made up of AddRef, Release, and QueryInterface. • AddRef and Release keep track of the objects connected to the component. • QueryInterface allows clients to determine if it can use a given interface with a component. It also retrieves the interface pointers.

  21. COM: COL • The Component Object Library contains much of the work of the COM system. • It maintains all of the GUID’s • It handles loading requested components by calling what the component needs.

  22. COM: Problems • Implementation Inheritance can inherit some of its functionality from another component • The problem is this is not clearly defined. If a parent or child component is changed it my mess up other components related to it.

  23. COM: Problems • Cost for using COM on Microsoft products is very low, but for non Microsoft products is very expensive. • COM doesn’t make distributed any easier it just redirects where this process is handled.

  24. CORBA • It is maintained by the Object Management Group, which is comprised of nearly all the major software developers.

  25. CORBA • CORBA handles network programming tasks such as object registration, location, and activation, request demultiplexing, framing and error-handling, etc. • Each service that an object provides is given by its interface which is defined by Interface Definition Language (IDL). • Object Request Broker (ORB) handles requests and delivers them from objects to the clients.

  26. CORBA: ORB • The ORB is a distributed service that sends requests to remote objects, finds that object and waits for it’s reply and gives it to the client. • The client is hidden from this process as it same method as calling a local object.

  27. CORBA: ORB • The ORB also maintains the Interface Repository (IR) which contains the IDL. • On the server side ORB regulates the running objects by turning on or off programs as they are needed.

  28. CORBA: DII • The Dynamic Invocation Interface are interpreted at run time an not compiled. • This allows the invocation of an operation of a new type. • There must be a way to retrieve the necessary information to use the DII.

  29. CORBA: Stubs • Stubs are what the client uses to interface with the ORB. • A client might invoke hundreds of instances but a new stub is created when the instance is of a different type

  30. CORBA: ORB Interface • It provides access to every ORB service except for client requests which go through the stubs and object requests which are done through the POA.

  31. CORBA: ORB Implementaion • The client-side architecture is simple • This allows for all scalability options are on the server side. • The ORB doesn’t require code to be in a specific spot so that ORBs can spread their work across vast networks or keep it all in one computer.

  32. CORBA: Interoperability • CORBA specifies an API to use which creates the ability to use code with different vendor’s with little effort. • CORBA 2.0 added IIOP network protocol that allowed communication of CORBA products over TCP/IP connections. • IIOP is used by other systems so that interoperability is possible with non-CORBA systems.

  33. CORBA: Services • These services support the distributed objects. • They operate on the ORB and have IDL interfaces • These include naming, events, transactions, properties, etc.

  34. CORBA: IDL • The Interface Definition Language doesn’t have a programming language but it maps to popular programming languages. • The IDL defines the interface very strictly so that it can easily pass requests between different programming language objects. • It is so strict that even if an ORD is different is can still easily communicate • The other objects are encapsulated so that a client can’t see other objects code or data.

  35. CORBA: Problems • CORBA calls are all the same so the simplest call must be the same as the most complex call. There is no limit on the complexity. • Since CORBA is regulated by the very large OMG, it is difficult to create standards because of the many different opinions.

  36. Questions?

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