Computer Science Notes SET-2

Computer Terminology: M to Z

Member Record: A record within a set, where that record has a dependent relationship with the owner of that set. 

Navigation: The process by which a program is coded to follow access paths defined by the data­base structure. 

Network: One or more collections of directed relationships between three or more units of data such that some units of data are considered owners while other are members, where each member may have more than one owner. 

Occurrence: A specific instance of the value of a unit of data. 

Optimal Third Normal Form: A collection of relations are in the optimal third normal form, where the number of relations used to define a given collection of data is at a minimum, and cache relation must not have any pair of attributes such that one member of the pair is strictly transitively dependent on the other in some relation. 

Owner Record: A record which determines the existence of a set, and with which any other records of that set have a dependent relationship. 

Physical Data: The data which the database management system presents to the operating system for storage or receives from it for processing.

Plexus Entry: A set of group relations in which every group except the entry-defining group can be subordinate to another group and participate in more general relations.

 Pointer Array: A collection of pointers associa­ted with an owner record and used to link it with the member records of a set. 

Primary Key: The domain or combination of domains of a given relation with uniquely identifies each type of that relation. 

Prime Attribute: Any attribute of a relation that participates in at least one candidate key of that relation. 

Privacy Key: A data-item whose contents are used by the DBMS to determine if a locked resource is to be made available to the run-unit that specified the privacy key value. 

Privacy Lock: A value known to the DBMS that is associated with a facility of data unit. 

Projection: The operation of selecting from a relation specified-domain and then removing any tuples which are now producing a. second more limited relation. 

Realm: A logical sub-division of the database into which records of specified types may be stored. 

Record-Occurrence: A single instance of a named collection of data-elements of data-aggre­gates. 

Record Selection Expression (RSE): The phrase specified in a source program that specifies the algorithm to be used by the DBMS to identify a specific database record. 

Record-Type: A named collection of zero, one or more data elements or data-aggregates. There may be an arbitrary number of occurrences in the database of each record type. 

Redundancy: A situation where there are multi­ple occurrences of a particular unit of data in a database. 

Relation: A relation exists between a group of sets, if each element in each set has a logical con­nection with the corresponding elements in the other sets. 

Relation Model: A logical view of data in which all data elements are grouped in relations of the third normal form. 

Relationship: A relation in which the ordering of domains is of no significance. Or A meaningful association between units of data. 

Reorganization: The process of rearranging the relative physical placement of data-units in the database. 

Repeating Group: A collection of data that occurs an arbitrary number of times within a record occurrence, may, consist of data-items, vectors and repeating groups. 

Requestor: An individual desiring to use the data in a database. 

Restriction: The operation of producing a subset of one relation, which contains all tuples that are in common with a second relation. 

Restructure: The process of adding to or delet­ing from the types of data-units and data-relation­ship represented in the database, or rearranging data-units which are components of larger data-units, and of making the corresponding changes to its schema. 

Roll-Back: The process of reversing recent activities of the system, to store some of or the entire database to its state at a previous point in time. 

Run-Unit: The execution of one or more pro­grams. Each run-unit is a separate entity serviced by the DBMS with its own user working area and communication locations. 

Schema: A complete description of the database in terms of the characteristics of the data and the implicit and explicit relationship between data-units. 

Second Normal Form: A relation is in second normal form if it is in first normal form and every non-prime attribute of the relation is fully depen­dent on each of its candidate keys. 

Self-Defining Data: A unit of data whose des­cription appears with its occurrence. 

Set: A named collection of related records repre­senting a one-to-many relationship between the owner and member records. 

Set Selection: The process by which the DBMS uses a specified algorithm to determine the appro­priate occurrence of set type for the purpose of inserting or accessing a member record. 

Subschema: A description of those data-Units and relationships from a database of interest to a particular program. 

System Communication Locations: The loca­tions used for interaction between the DBMS and a run-unit; these include currency status indicators and error status information. 

Temporary Area: A sub-division of addressable storage space in the database, a different occurrence of which is provided for each run-unit opening it, and which is retained only during the life of the run-unit. 

Third Normal Form (TNF): A relation is in third normal form if and only if its non-key domains (if any) are mutually independent and fully inde­pendent on its primary key. 

Transposed File: A storage organization in which data-items of a given type are stored as a vector, with each of the data-items from any one record occurrence held at the same relative position in each of the vectors concerned. 

Transitive Dependence: Dependence between attributes which is indirectly implicit, due to direct functional dependence with other attributes. 

Transparency: The shielding of the application from changes to the database. 

N-Tuple: An occurrence of n related data-elements such that each is a corresponding member of n domains which form a relation. 

Union: The operation of combining two rela­tions with all domains in common, together with elimination of any identical tuples. 

Union-Compatible Domains: Domains of the same degree where each pair of corresponding do­mains are either both of integer elements of both of character string elements. 

User Working Area (UWA): The locations where all data provided by the DMS in response to a call for data is delivered, and where all data to be picked up by the DMS must be placed.

 Vector: A one-dimensional, ordered collection of data-items, all of which have identical charac­teristics.#