A Dictionary of DBMS Terms Access Plan Access plans are generated by the optimization component to implement queries submitted by users. ACID Properties ACID properties are transaction properties supported by DBMSs. ACID is an acronym for atomic, consistent, isolated, and durable. Address A location in memory where data are stored and can be retrieved. Aggregation Aggregation is the process of compiling information on an object, thereby abstracting a higher-level object. Aggregate Function A function that produces a single result based on the contents of an entire set of table rows. Alias Alias refers to the process of renaming a record. It is alternative name used for an attribute. 700 A Dictionary of DBMS Terms Anomaly The inconsistency that may result when a user attempts to update a table that contains redundant data. ANSI American National Standards Institute, one of the groups responsible for SQL standards. Application Program Interface (API) A set of functions in a particular programming language is used by a client that interfaces to a software system. ARIES ARIES is a recovery algorithm used by the recovery manager which is invoked after a crash. Armstrong’s Axioms Set of inference rules based on set of axioms that permit the algebraic mani- pulation of dependencies. Armstrong’s axioms enable the discovery of minimal cover of a set of functional dependencies. Associative Entity Type A weak entity type that depends on two or more entity types for its primary key. Attribute The differing data items within a relation. An attribute is a named column of a relation. Authorization The operation that verifies the permissions and access rights granted to a user. Base Table Base table is a named relation corresponding to an entity in the conceptual schema, whose tuples (rows) are physically stored in the database. A Dictionary of DBMS Terms 701 Bitmap Index A compact, high speed indexing method where the key values and the condi- tions are compressed to a small size that can be stored and searched rapidly. BLOB BLOB is an acronym for Binary Large Object. BLOB is a data type for fields containing large binary data such as images. Boyce–Codd Normal Form A relation in third normal form in which every determinant is a candidate key. Bucket With reference to hash file, Bucket is the unit of a file having a particular address. Buffer Buffer an area in main memory containing physical database records trans- ferred from disk. Candidate Key Any data item or group of data items which identify uniquely tuples in a relation. Cardinality The number of tuples in a relation. Cartesian Product All of the possible combinations of the rows from each of the tables involved in a join operation. CASE Tool CASE is an acronym for computer-aided software engineering. CASE tools support features for drawing, analysis, prototyping, and data dictionary. CASE tool facilitate database development. 702 A Dictionary of DBMS Terms Chasm Trap A chasm trap exists where a model suggests the existence of relationship between entity types, but the pathway does not exist between certain entity occurrences. Client An individual user workstation that represents the front end of a DBMS. Client/Server Architecture Client/Server architecture is an arrangement of components among computers connected by a network. Clustered Index An index in which the logical or indexed order of the key values is the same as the physical stored order of the corresponding rows. CODASYL Conference on Data System Languages. Concurrent Access Performing two or more operations on the same data at the same time. Concurrency Control Concurrency control is the control on the database and transactions which are executed concurrently to ensure that each transaction completed healthy. Composite Key A candidate key comprising more than one attribute Composite Index An index that uses more than one column in a table to index data. COMMIT To control transactions, SQL provides this command to save recent DML changes to the database. A Dictionary of DBMS Terms 703 Condition Box A special box used by QBE to store logical conditions that are not easily expressed in the table skeleton. Constraints Constraints are conditions that are used to impose rules on the table. Conceptual View The logical database description in ANSI/SPARC DBMS architecture. Concurrent Access Two or more users operating on the same rows in a database table at the same time. Correlated Subquery In SQL, a sub query in which processing the inner query depends on data from the outer query. COUNT An aggregate function that returns the number of values in a column. Cursor An SQL feature that specifies a set of rows, an ordering of those rows and a current row within that ordering. Data Data is a representation of facts, concepts or instructions in a formalized manner suitable for communication, interpretation or processing by humans or automatic means. Data Abstraction Data abstraction means the storage details of the data are hidden from the user and the user is provided with the conceptual view of the database. 704 A Dictionary of DBMS Terms Database Database is the collection of interrelated data. Data Definition Language (DDL) The language component of a DBMS that is used to describe the logical structure of a database. Data Manipulation Language (DML) A language component of a DBMS that is used by a programmer to access and modify the contents of a database. Database Instance The actual data stored in a database at a particular moment in time. Database State Database state refers to the content of a database at a moment in time. Database Management System General purpose software used to maintain the database. Database System A database system means both a DBMS plus a database. Database Administrator A person or group of people responsible for the design and supervision of a data base. Database Recovery The process of restoring the database to a correct state in the event of a failure. Database Security Protection of the database against accidental or intentional loss, destruction, or misuse. A Dictionary of DBMS Terms 705 Data Mining Data mining is the process of discovering implicit patterns in data stored in data warehouse and using those patterns for business advantage such as predicting future trends. Data Model Collection of conceptual tools for describing data and relationship between data. Data Dictionary Centralized store of information about database. Data Warehouse Data warehouse is a central repository for summarized and integrated data from operational databases and external data sources. DB2 An IBM relational database system. DBTG Database Task Group. Deadlock The situation where each of two transactions are waiting indefinitely for the other transaction to release the resources it requests. Degree of a Relation The number of attributes in the relation. Denormalization Denormalization is the process of combining tables so that they are easier to query. Denormalization is opposite to normalization. Denormalization is done to improve query performance. 706 A Dictionary of DBMS Terms Derived Attribute Derived attributes are the attributes whose values are derived from other related attribute. Determinant An attribute or set of attributes on which the value of one or more attributes depend. Distributed Database A database located at more than one site. Domain The set of all possible values for a given data item. Domain Integrity Data integrity that enforces valid entries for a given column Domain Relational Calculus Domain Relational Calculus is a calculus that was introduced by Edgar F. Codd as a declarative database query language for the relational data model. DDL Data Definition Language is used to define the schema of a relation. DML Data Manipulation Language is basically used to manipulate a relation. Dual A virtual table automatically created by Oracle along with the data dictionary. It has one column, DUMMY, defined to be VARCHAR2(1), and contains one row with a value of “X”. Embedded SQL An application structure in which SQL statements are embedded within pro- grams written in a host language like C, JAVA. A Dictionary of DBMS Terms 707 Encapsulation Hiding the representation of an object is encapsulation. Entity An object that exist and is distinguishable from other objects. Entity Class A set of entities of the same type. Entity Instance Entity instance is a particular occurrence of an entity. Entity Integrity (Table Integrity) Integrity that defines a row as a unique entity for a particular table and ensures that the column cannot contain duplicate values. Equijoin A join operator where the join condition involves equality. ER Model ER stands for Entity-Relationship model. ER Model is based on a perception of a real world that consists of collection of basic objects called entities and relationships among these objects. EER Model EER stands for Enhanced ER model. EER model is the extension of origi- nal model with new modeling constructs. The new modeling constructs are supertype, subtype. Exclusive Lock A lock that prevents other users from accessing a database item. Exclusive locks conflict with all other kids of locks such as shared locks. 708 A Dictionary of DBMS Terms Fantrap A fantrap exists where a model represents a relationship between entity types but the pathway between certain entity occurrences is ambiguous. File A file is a collection of records of the same type. File Organization Methods used in organizing data for storage and retrieval such as sequential, indexed sequential, or direct. First Normal Form A relation is in first normal form if it contains no repeating groups. Flat File A file in which the fields of records are simple atomic values. Foreign Key Attribute or set of attributes that identifies the entity with which another entity is associated. Fourth Normal Form A relation is in fourth normal form if it is in BCNF and contains no multi- valued dependencies.