what is a DS?
a collection of d/t components running on d/t programing languages, OS and computer arc
what is the use of middleware for DSs?
- is a layer b/n OS and DS applications that provides a common runtime env’t, there by providing homogeneity and abstraction
___________ is used to mask heterogeneity of DSs?
middleware
___________ is the SW that makes the HW usable?
OS
___________ is the SW that makes DS programmable?
middleware
what problems does middleware bring to dev’t?
MUM D
- more sw that has to be bought, tested and learnt by the programmer
- does not provide guarantees on bandwidth used and time taken
- marshaled code by the middleware may not be as efficient as code written by developer
- may be unwanted or unnecessary
what are categories of middleware?
- transactional : IBM’s CICS
- MOM : sun’s JSM
- procedural : RPC
- object based : comm b/n obj : CORBA, COM
- component based : EJB
what is CORBA?
common obj req broker arch
- is a middleware platform that supports standardized OO arch for applications
- developed by OMG [ obj management group ]
what is OMG’s mission?
- to establish industry guidelines and object management specification
what is the use of a broker in CORBA?
- is an intermediary that facilitates communication b/n client and server
- it separates a component’s interface from its implementation
what is the strong point of COBRA?
Its a distributed middleware, so it allows applications to communicate even if they are:
- on d/t computers
- on d/t OS
- on d/t processor
- implemented using d/t programming languages
explain how CORBA enhances the client server arch?
- extends computing paradigms like RPC to distributed computing
- it adds OO features: interface, messages, inheritance and polymorphism
- an application can be both a client and a server at the same time
- server : process that hold objects
- client : process that makes calls to objects
- supports both asynchronous and defered synchronous communications
what are the main features of CORBA?
- object req broker [ ORB ]
- stubs and skeletons
- OMG’s interface definition language [ IDL ]
- static and dynamic invokations
- internet inter ORB protocol [ IIOP ]
- object adaptors
- interface repository
_____________ is the heart of CORBA?
object req broker
explain ORB.
- facilitates comm b/n client and obj implementation [ code that imp the obj ]
- requests to an obj are made using ORB
- hides an obj’s:
- location
- implementation
- comm mechanism
- execution state
_____________ isolates the client and the object implementation from the ORB?
IDL - interface definition language
how is remote invocation handled in CORBA?
- passed from ORB of client to ORB of obj implementation
explain interface definition language?
- IDL describes an object by using its interface [ what the obj does ]
- interface : set of named operations and their parameters
- IDL is implementation [ how obj works ] independent and interface dependent
- types: float, double, char, enum, string { arr, struct }
- IDL is language independent:
—— provides a standardized mapping to C, C++, Java ….
_____________ are used in CORBA’s static invocations?
stubs and skeletons
explain static method invokation?
- is the process in w/c a client invokes operation directly on the client stub
- the IDL compiler generates the stub and skeleton
- the IDL compiler adds implementation code to the server and instantiates objs on the server
- distributed system lay yalew stub skeleton diagram
what is interface repository?
- is a CORBA service that manages an object’s implementation.
- the orb needs to know how to start an object whose interface is not known at compile time
- dynamic method invocation
what is dynamic method invocation?
- allows CORBA clients to invoke operations on any objects with knowing the obj’s interface
- obtains interface name and method description from the interface repository.
Compared to static method invocation : - more complex
- harder to program
- slower
- less robust type checking
list services provided by CORBA?
ONE REQ T TCP
- object life cycle
- naming
- event
- r/n ship
- externalization
- query
- trading
- transaction
- concurrency
- property
which CORBA service coordinates transformation of obj to and from external media?
externalization
