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GLOBE Distributed Shared Object

GLOBE Distributed Shared Object. INTRODUCTION. Globe stands for GLobal Object Based Environment. Globe is different from CORBA and DCOM that it supports a huge number of users across the Internet and still provides distribution transparency.

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GLOBE Distributed Shared Object

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  1. GLOBE Distributed Shared Object

  2. INTRODUCTION • Globe stands for GLobal Object Based Environment. • Globe is different from CORBA and DCOM that it supports a huge number of users across the Internet and still provides distribution transparency. • The most important design goal of Globe is scalability. • Each object is in full control of its distribution strategies across its own replicas. • Hence, such a middleware platform of distributed shared objects is best suited for large scale applications of the future.

  3. ARCHITECTURE

  4. A local object consists of at least four subobjects: Semantics subobject. • This is a local subobject that implements the actual semantics of the distributed object. • For example: GlobeDoc. Communication subobject. • It is responsible for handling communication between parts of the distributed object that reside in different address spaces. • It may offer messaging passing primitives for connection oriented and connectionless communication, multicast facilities.

  5. Replication subobject. • It implements the actual distribution strategy for an object. • The replication subobject has a standard interface. Control subobject. • It bridges the gap between the user defined interfaces of the semantics subobject, and the standard interfaces of the replication subobject. • It takes care of method invocations from client processes.

  6. PROCESS TO OBJECT BINDING The procedure takes place as follows: • To bind to an object, a process must pass the name of that object to a naming service. • The naming service returns an object handle which is globally unique and location independent. It can be used as a systemwide object reference. • The object handle is given to location service which returns a set of contact addresses for a single object. • The protocol information is used to load and instantiate classes from a (trusted) class repository. • The local object is initialized and through this local object, other local objects are contacted that form a part of the DSO.

  7. COMMUNICATION • To communicate, both parties first bind to some common DSO, and then perform operations on it. • The user just invokes a method on a local object and the object itself manages the replication transparently. • When an invocation completes, no more activity will take place in the DSO, except the activity caused by other invocations. • Hence, Globe objects are said to be passive.

  8. NAMING • The naming service in Globe is based on DNS. • To make use of DNS, a Globe name is first transformed into a DNS name. • For example: we transform a name such as globe://nl/vu/cs/object/foo into foo.object.cs.vu.nl. which is then passed to the local DNS name resolver. The resolution eventually reaches a Globe name server that can handle that part of a name that has not yet been resolved.

  9. LOCATION • The location service stores every DSO’s contact addresses and maintains a mapping of every object handle to a set of contact addresses. • To ensure scalability, the location service should exploit locality.

  10. REPLICATION • Globe incorporates a replication subobject in each local object. • Interfaces of a replication subobject are standardized which results in high degree of flexibility. FAULT TOLERANCE • Fault tolerance in Globe is achieved mainly through replication. • To recover after a failure, globe object server ensures that all local objects are made persistent.

  11. SECURITY • It concentrates on protecting a single DSO against security attacks. • Security is partly handled by a separate security subobject. It communicates with local security services like Kerberos, SESAME and considers various security issues with respect to communication, invocation of semantics subobject and replication.

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