meow 327 quiz 3

Distributed Objects

Software modules that work together but reside on different computer systems, communicating via remote method invocation.

Remote Method Invocation (RMI)

A Java-based API allowing objects in different JVMs to interact as if they were local.

Encapsulation

Objects hide implementation details and expose only defined interfaces for interaction.

Marshalling

converts objects into a format suitable for transmission

What makes an object useful as a basis for defining persistence, protection and distribution?

objects are self contained and independent, self describing and are abstract and encapsulated

Unmarshalling

The process of converting a serialized data stream back into an object or data structure. and is used in distributed systems to reconstruct transmitted data on the receiving end.

Stub

a client-side proxy that sends method calls to a remote object

Skeleton

A server-side component in Remote Method Invocation (RMI) that receives remote calls from client stubs, unmarshals the request, invokes the corresponding method on the actual remote object, and sends the response back to the client.

Object References in Distributed Systems

A unique identifier used to locate remote objects across a distributed system

Remote Procedure Call (RPC)

A protocol allowing function calls across a network as if they were local function calls.

Component Object Model (COM/DCOM)

Microsoft’s standard for distributed objects, enabling interoperability across Windows applications.

Common Object Request Broker Architecture (CORBA)

A middleware standard allowing objects to communicate across different programming languages and platforms.

Enterprise Java Beans (EJB)

A Java-based technology for building scalable, distributed applications using RMI.

Remote objects must reside in the same process as the invoking client.

False

Marshalling is the process of converting an object into a format suitable for transmission.

True

Java RMI supports automatic garbage collection of remote objects.

True

RPC and RMI are identical in implementation.

False

Distributed objects can be migrated across networks to balance load.

True

What role does a stub play in RMI?

A stub acts as a local proxy for a remote object, forwarding method calls.

Why is object migration important in distributed systems?

It improves performance by reducing network latency and enables load balancing.

What is the difference between RMI and RPC?

RMI supports object-oriented interactions, while RPC is procedural and does not involve objects.

How does CORBA facilitate distributed object communication?

It provides a standard interface definition language (IDL) to enable cross-platform object communication.

How does encapsulation benefit distributed objects in a system?

Encapsulation hides implementation details, ensuring that only defined methods are accessible, which enhances security and modularity.

Why is persistence an important property of distributed objects?

Persistence allows objects to exist beyond the execution of a single program, making them useful for long-term storage, caching, and state management.

How does location independence impact distributed object interactions?

Objects can be accessed without needing to know their physical location, simplifying system design and improving scalability.

Why is object replication useful in distributed systems?

enhances fault tolerance and load balancing by maintaining multiple copies of an object across different nodes.

What is dynamic binding in distributed systems, and why is it beneficial?

Dynamic binding allows objects to discover and interact with other objects at runtime, making distributed systems more flexible and adaptable.

What are some challenges in making distributed objects interoperable across different programming languages?

Different languages have varying data structures, type systems, and communication protocols, requiring middleware like CORBA to standardize interactions.

Why do data format differences present a problem in distributed systems?

Different systems may use different encoding formats (e.g., little-endian vs. big-endian) requiring external data representation (e.g., marshalling) to ensure compatibility.

How does failure recovery work in distributed object systems?

Failure recovery involves techniques like state checkpointing, logging, replication, and exception handling to restore object state after crashes.

What security concerns arise when using remote objects in a distributed environment?

Concerns include unauthorized access, data interception, and malicious object manipulation, which are mitigated using authentication, encryption, and access control mechanisms.

What role does the client play in a distributed object system?

The client invokes methods on remote objects managed by a server using remote method invocation (RMI) or remote procedure calls (RPC).

How are remote objects managed by the server in a distributed system?

The server maintains object instances, handles client requests, processes remote method calls, and returns results to the client.

Why are object references crucial in remote communication?

Object references provide a way to uniquely identify and locate remote objects across a distributed network, enabling seamless invocation of remote methods.

What are the key differences between RMI and RPC in distributed systems?

RMI is object-oriented, allowing method calls on remote objects, while RPC is procedural and supports function calls between distributed components.

What makes the Emerald system unique among distributed object models?

Emerald integrates distribution directly into its language and runtime, enabling seamless object mobility and transparent remote invocation.

How does object migration work in the Emerald system?

Objects can move dynamically between nodes while maintaining references and execution context, improving performance and flexibility.

What is the advantage of using pass-by-reference in Emerald’s remote method calls?

Pass-by-reference allows objects to interact without duplicating large amounts of data, improving efficiency and reducing network overhead.

What is RMI, and how does it support distributed objects in Java?

RMI is a Java API that enables objects in different JVMs to invoke methods remotely, supporting automatic garbage collection and serialization.

How does COM/DCOM facilitate distributed object communication in Windows?

COM (Component Object Model) provides a binary standard for object interaction, while DCOM (Distributed COM) extends it to work across networks.

What is CORBA, and how does it enable language-agnostic distributed computing?

CORBA (Common Object Request Broker Architecture) provides an interface definition language (IDL) that allows objects written in different languages to communicate.

How does EJB (Enterprise Java Beans) extend RMI for enterprise applications?

EJB builds on RMI, providing transaction management, security, and scalability for large-scale distributed Java applications.

Why are web services and SOAP important in distributed systems?

They enable platform-independent communication using standardized XML-based messaging over HTTP, allowing different systems to exchange data seamlessly.

Object: Object references
Distributed objects: Remote object references

globally unique reference for a distributed object; may be passed as a parameter

Object: interfaces
Distributed objects: remote interfaces

Provides an abstract specification of the methods that can be invoked on the remote object; specified using an interface destination language (IDL).

Object: actions
Distributed objects: Distributed actions

Initiated by a method invocation, potentially resulting in invocation chains remote invocations use RMI.

Object: Exceptions
Distributed objects: Distributed Exceptions

Additional exceptions generated from the distributed nature of the system, including message loss or process failure

Object: garbage collection
Distributed objects: distributed garbage collection

Extended scheme to ensure that an object will continue to exist if at least one object reference or remote object reference exists for that object, otherwise it should be removed. Requires a distributed garbage collection algorithm.

Can we use distributed objects as a basis for interoperability among software modules written in different languages?

Yes, distributed objects can enable interoperability among software modules written in different languages using middleware like CORBA, Web Services, or gRPC, which standardize communication. However, challenges like data type mismatches and serialization overhead must be managed.

what does it mean when objects are self-contained and independent

Objects are a useful granularity for persistence, caching, location, replication, and/or access control.

what does it mean when objects are self-describing

Object methods are dynamically bound, so programs can import and operate on objects found in shared or persistent storage.

what does it mean when objects are abstract and encapsulated

It is easy to control object access by verifying that all clients invoke the object’s methods through a legal reference. Invocation is syntactically and semantically independent of an object’s location or implementation.

What weakness comes with Emerald’s distribution being fully integrated into the language, its implementation and even its type model?

it combines language issues and system issues that should be separated.

How to preserve inter-object pointers across migration?

Use an object table with descriptors for each object, updating references to point to the new location when an object moves.

How to keep threads “sticky” with migrating objects?

Ensure threads follow the migrating object by updating their execution context to reflect the new location of the object.

How to maintain references in stack activation records?

Update stack activation records to point to the new location of the migrated object, ensuring continuity in method execution.

How to maintain linkages among activation records?

Adjust linkages in activation records to reflect the new object locations, preserving the call chain and execution flow.

What is the benefit of having client and server objects in different processes?

it enforces encapsulation due to concurrency and heterogeneity of RMI calls.

remote objects

can receive remote invocations

Remote Object Reference

A unique identifier used across a distributed system to refer to a specific remote object.

Remote Interface

An interface that specifies which methods of a remote object can be invoked by objects in other processes.

In order for the client object to invoke methods on the server, what must it first do?

look up the name of the server in the registry using the java.rmi.Naming class to lookup the server name

What is the server specified as?

URL in the form (rmi://host:port/name ) with Default RMI port as 1099.