middleware and distributed systems

middleware

manager of resources offering its applications to efficiently share and deploy those resources across a network; operating system of distributed systems

openness

goal of middleware

wrappers

interface around an existing component which enables it to be used by a different system without modifying its internal code

interceptors

breaks the operation flow and can modify the request or response, log information, handle errors, or do other tasks

adapters

wrappers are also known as _

interfaces

wrappers are special components that provide _ to client

modern services interfaces for legacy code/systems

interface wrappers transform client requests to “implementation” at the component-level which can provide _

incompatible

wrappers solve the problem of _ interfaces

object adapters

component that allows applications to invoke remote objects, although those objects may have been implemented as a combination of library functions operating on the tables of a relational database

extensibility

which is crucial for achieving openness, used to be addressed by adding wrappers as needed

brokers

common intermediary / a centralized component that handles all the accesses between different applications

message broker

software that enables applications, systems and services to communicate with each other and exchange information

RPC and RMI

interceptors enable _

adapting middleware

interceptors are a primary means for _ to the specific needs of an application

request-level interceptor

simply call invoke for each of the replicas

multiple replicas

request-level interceptors deals with requests in a broader sense, interacting with _ (or servers) and ensuring the request is processed appropriately

message-level interceptor

assist in transferring the invocation to the target object

details

message-level interceptors focuses on message-level _, ensuring invocation is transferred correctly to the target object

modifiable middleware

middleware may not only need to be adaptive, but should be able to purposefully _ it without loss of availability (replacing components at runtime, dynamically constructing middleware from components)