Topology is a term used to describe the overall configuration of the Oracle Net Services distributed databases, including all clients and Oracle servers.
In large topologies it is not uncommon to find different communications protocols (the protocol is the software layer that resides on top of the topology), as the network may span different operating environments, such as DEC, mainframes, and Novell. In theory, any of the following protocols can run under any topology. Due to the overwhelming use of the UNIX operating system, the most popular protocol has become TCP/IP, but Oracle supports some of the more obscure protocols as well.
- DNA (DecNet): DEC's Distributed Networking Architect: Introduced in 1975 by DEC for use in the VMS operating system.
- TCP/IP: Transmission Control Protocol / Internet Protocol: TCP is a standard protocol that enables a process on one machine to send a stream of data to another machine. IP is protocol that provides a packet delivery service across a network.
- SNA: IBM's System Network Architecture: Introduced in 1974, SNA is a standard protocol and the one most commonly used today.
- X.25: Developed by Bell Canada, X.25 is the basis for ISDN and the OSI model for open systems.
Again, while Oracle Net Services has the ability to support cross-protocol communications, the vast majority of Oracle Net Services implementations utilize TCP/IP.
The topology data model of Oracle Spatial lets you work with data about
- nodes,
- edges, and
- faces
in a topology.
For example, United States Census geographic data is provided in terms of nodes, chains, and polygons, and this data can be represented using the Spatial topology data model.
You can store information about topological elements and geometry layers in Oracle Spatial tables and metadata views. You can then perform certain Spatial operations referencing the topological elements, for example,
finding which chains (such as streets) have any spatial interaction with a specific polygon entity (such as a park).
The Spatial data structures and data types support the topology data model which are required to populate and manipulate the structures.
You can use this information to write a program to convert your topological data into formats usable with Spatial.
In general usage, a packet is a unit of information transmitted as a whole from one device to another on a network.
In packet-switching networks, a packet is defined more specifically as a transmission unit of fixed maximum size that consists of binary digits representing
- data,
- a header containing an identification number,
- source and destination addresses, and
- sometimes error-control data.
In the next lesson, the evolution of databases from centralized to distributed will be discussed.
