461 - Glossary

Copyright © 2002 Katrin Becker 1998-2002 Last Modified May 19, 2000 04:36 PM

Cpsc 461 Glossary

Block: smallest amount of data that can be read from or written to secondary storage at one time. Often generalized to mean any chunk of data that can be treated as a unit (for reading, writing, organizing). We will distinguish between disk blocks (physical) and program defined blocks (logical).

Blocking: the process of grouping several components into one block

Bound Keys: keys in a record that are attached to the physical (eg. byte offset) location of a record

Buffering: Software interface that reconciles blocked components of the file with the program that accesses information as single components. A buffering interface is of one of two types: blocking routine or deblocking routine.

Clustering: grouping file components according to access behaviour

Double Buffering: having two buffers so one can be filled while the other is being processed

Entry-Sequenced File: a file whose records are 'sorted' in the same order in which they were appended

Field: is a unit of information (logical rather than physical - conceptual tool)

File: collection of bits, usually logically related

Inverted List: a list used to access an index

Key: a field in a record used as ID or to control its use

Locality: a property that describes the physical proximity (closeness) of a set of records or blocks

Logical File Structure: how we (as programmers) see the file

- usually thought of as being in one piece
- can be anything (ASCII, pictures, records, music)
- sub-structure imposed by software that is uses

Logical Write: writing one component to the block-sized buffer

Metadata (meta X ::= X about X) (header) data in file describing primary data in file

Physical File Structure: how O/S sees the file (in UNIX this is always just a stream of bytes)

- organization of actual bytes on storage medium may be quite different from logical organization
- It's important to remember the distinction between the physical files and devices and the logical structure of the same thing.

Physical Write: writing one block to the external file

Pinned Records: one that can't be moved because other records contains 'physical' pointers to it; if it's moved someone else's pointers are left dangling

Processor Bound: A process where more time is taken to process a block than is taken to read or write the block. In such a case, the entire process can only be made faster by increasing the efficiency of the processing part.

Record: is collection of related fields treated as a unit

Stream Files: basically strings of bytes