Distributed data processing – data processing carried out in a distributed system in which each of the technological or functional nodes of the system can independently process local data and make appropriate decisions. When performing individual processes nodes of a distributed system can exchange information through communication channels in order to process data or obtain the results of analysis of mutual interest to them.
A distributed system is a set of independent computers (in the sense of processes running on each computer) that appear to their users as a single unified system.
There are two important points in the definition: a) the hardware parts of the distributed system are autonomous, and b) the users think that they are dealing with a unified system.
In accordance with the presented requirements, when building distributed systems, tasks arise to ensure:
sharing of user access to the system resources;
transparency of the system;
openness of the system;
scalability of the system.
An open distributed system is a system offering services, which are called using standard interfaces described by Interface Definition Language (IDL). The description accurately reflects the names of available functions, types of parameters, types of return values, exceptional situations that may be caused by the operation of the service, etc.
System scalability is measured in three different ways.
- A system can be scalable in relation to its size. This means the ease of connecting additional users and resources to it.
- the system can scale geographically, i.e. users and resources can be dispersed in space.
- the system can be scalable in an administrative sense, i.e. it can be easily managed across multiple independent organizations.
Information distributed systems are built in layers:
1) a presentation layer,
2) application logic layer,
3) resource management layer.
Layers can be abstract, but can be clearly visible in software as separate subsystems.
Information systems must communicate with other systems. Much of the communication involves transforming information and presenting it to users. The components of the information system that provide these activities form the presentation layer. Clients can be completely external with respect to the system and independent from it, then they are not its presentation layer (a network navigator is a client, it only shows a document, a network server is its presentation layer). The client and the presentation layer can be merged together, which is typical for client/server systems where there is a program that simultaneously acts as a presentation layer and a client (an applet).
Information systems carry out data processing by a program that implements the operations requested by the client through the presentation layer. Sometimes these programs are called services offered by information systems. Depending on the complexity of the logic performed, this layer may be called a business process, business logic, business rules or just a server. All of these names refer only to specific implementations.
An information system needs data to operate, housed in databases and file systems. The resource management layer deals with a variety of data sources, regardless of the specific nature of those sources. This makes it possible to recursively build information systems consisting of other information systems as components.
In practical implementations, the conceptual designs of layers can be combined in various ways. In these cases, we speak not of layers but of tiers. There are 4 main types of information systems known, distinguished by the number of tiers that comprise them:
u one-,
u two-tier
u three-tiered
u multilayer systems.
The number of links in a program with the client-server architecture is determined by the level of integration of the three program layers. A single-layer program is such a program in which the three layers are tightly interconnected. In particular, the presentation layer contains detailed information about the database structure. The application layer is often intertwined with both the presentation and service layers. All three layers, including the database processor, almost always run on the same computer.