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GLOSSARY ATC The acronym, ATC, stands for ALLBASE/Turbo CONNECT. The terms Turbo CONNECT and ALLBASE/Turbo CONNECT are synonymous with IMAGE/SQL. The acronym, ATC, appears in error messages for IMAGE/SQL (for example, ATCERR or ATCWARN). ATCINFO A permanent privileged file containing mapping information about data types and user security. By default, it is named DBEnvironment-nameCR. If you want to set a file equation for this file, you must do so before attaching any TurboIMAGE/XL databases. ATCLOG A temporary unnumbered ASCII file. If IMAGE/SQL utility logging is on (the default), all IMAGE/SQL utility commands are written to this file. If it does not already exist, it is created. If it exists, log records are appended to it. By default, it is name ATCLOG. However, you can set a file equation to change the name of this file. ATCUtil Another name for the IMAGE/SQL utility program. Attributes A characteristic of a data element considered during database design. As you organize your data, you arrange it into categories that possess similar attributes. The categories are known as entities. Authority Permission to access specific objects for specific purposes within a DBEnvironment. Authorization Group See Group. Base Table Table upon which a view is based. Check Constraint An integrity constraint that enforces a condition that must not be false for the columns of a table. Any value you attempt to insert into a column that has a check constraint defined on it must either satisfy the condition or be NULL. Class Special category of IMAGE/SQL owner that is neither a particular DBEUserID nor a group. You do not explicitly create a class; you create it implicitly by creating objects owned by it. A class does not have members like a group. Objects owned by classes can be dropped or modified only by a DBA. A class does not have a password associated with it. Column Vertical division within a database table. Analogous to an item in a TurboIMAGE/XL dataset. Column Authorization Permission to update a specific column within a table. Column List One or more columns specified as part of a query result. Concurrency The ability of multiple users to access the same database files simultaneously. Concurrency is regulated by locking, which controls the degree of concurrent access permitted--from exclusive read or write access to shared read with concurrent updates. Constraint A condition placed upon a column or table that requires values in the column or table to meet certain conditions before a row can be inserted or deleted. Two types supported by IMAGE/SQL are unique constraints and referential constraints. Data Analysis Study of raw data before building a database. Concerns the kind of data that is to be stored and how the data is to be used. Database A structured arrangement of data elements designed for the easy selection of information. In IMAGE/SQL, a database is a collection of tables and views having the same ownership in a DBEnvironment. A DBEnvironment may contain several databases. Database Administrator (DBA) The individual with DBA authority who creates and maintains objects in a DBEnvironment. DBA authority permits the use of certain restricted SQL and SQLUtil commands or options and also confers co-ownership of all the objects in a DBEnvironment. Database Design The creation of a specific arrangement of data in tables or data sets with an appropriate security structure. Data Control Language The set of SQL statements that control access to data. This includes the ADD, REMOVE, GRANT, and REVOKE statements, as well as the statements to create, manage, and drop authorization groups. Also known as DCL. Data Manipulation The process of accessing data within a database. Data Manipulation Language The set of SQL statements that access data. This includes the actions of selecting data, inserting rows, updating columns, and deleting rows. Also known as DML. Data Type A kind of data that can be stored in database tables. Valid types are CHARACTER, VARCHAR, INTEGER, DECIMAL, FLOAT, DATE, TIME, DATETIME, INTERVAL, BINARY, and VARBINARY. LONG varieties of BINARY and VARBINARY are also available. See Chapter 3 for a maping of these SQL data types to TurboIMAGE data types. DBA Authority The most powerful authority within an IMAGE/SQL DBEnvironment. Includes the authority to grant or revoke all authorities for other users. DBA authority implies co-ownership of all objects within the DBEnvironment. The creator of the DBEnvironment is automatically a DBA. DBC (Database Creator) The creator of the TurboIMAGE/XL database. You must be either the database creator or give the TurboIMAGE/XL database maintenance word to attach a database to a DBEnvironment. Commands that add users, or display or modify user information can only be executed by the DBC. DBECon File DBEnvironment Configuration File. This contains startup parameters for the DBEnvironment. The contents of this file are initially determined at the time you issue the START DBE NEW statement. You can modify some of these parameters using SQLUtil, and you can override some of them with the START DBE statement. DBECreator The individual who issues the START DBE NEW statement. See DBC. DBEFileSets Logical grouping of DBEFiles. DBEnvironment A collection of files containing one or more databases. Files include the DBECon file, which holds startup parameters and log file names; DBEFile0, which contains the system catalog; and log files. A DBenvironment may also contain additional DBEFiles for table and index data. The DBEnvironment is the maximum scope of a transaction within IMAGE/SQL. DBEFiles Operating system files that hold DBEnvironment data. DBEFiles have both physical names (operating system names) and logical names by which the files are known internally to the IMAGE/SQL system catalog. DBEUserID A login name and account name joined with the character '@'. One type of owner of database objects. Embedded SQL Programming An application program incorporating SQL statements for programmatic access to IMAGE/SQL databases. Entities Basic subdivision of data elements in database design. Each entity is a thing or event about which information is kept in the database. For each entity, there is at least one attribute that uniquely identifies a data element as belonging to the entity. Explicit Locking Locking of tables in transactions by the use of the LOCK TABLE statement. Expression Specifies a value. The most common sources of values are columns in a table or host variables in an application program. Expressions are used to identify columns or rows or to define new values for columns. Group Authorization group. Membership in a group is used to confer common ownership or common authorization for other objects in the DBE. You create a group explicitly using the CREATE GROUP statement, then you add users to it. You can then grant authorizations to the group or revoke authorizations from the group. You can also use the group name for the ownership of database objects. Logging The use of log files to record operations that modify database files. IMAGE/SQL Database A TurboIMAGE/XL database attached to an SQL DBEnvironment. Implicit Locking Locking of tables in transactions according to table type and isolation level. For example, PRIVATE tables are locked exclusively for all access; PUBLIC tables are locked exclusively only for write operations. Integrity Constraint A constraint placed on the columns of a table to ensure that a database contains only valid data. Two types are the referential constraint and the unique constraint . Isolation Level The degree of separation enforced between the transactions of different users. There are four levels: Repeatable Read (RR), Cursor Stability (CS), Read Committed (RC), and Read Uncommitted (RU). You specify an isolation level in the BEGIN WORK statement. ISQL The interactive interface to Hewlett-Packard's relational database products. ISQL is the tool you use for queries as well as for loading and unloading data and other database administration tasks. Joining A query that accesses data from two or more relational tables at a time. A join column is a column that occurs in both tables of a join (often it is a key column) and contains similar values in both tables. Key One or more columns on which an index, hash structure, or integrity constraint are based. Locking A technique for concurrency control through which Hewlett-Packard's relational databases restrict access to data by one individual when the data is being used by another. Locks are of three types: shared, exclusive, or shared with intent to become exclusive. Lock type is determined by the type of table being accessed and by the kind of operation the user is performing. Locks are released when a transaction ends with a COMMIT WORK statement. See also Explicit Locking and Implicit Locking. Logging The use of log files to record operations that modify database files. Logging is of two kinds: nonarchive logging , and archive logging . Both kinds permit you to roll back incomplete transactions following a system failure. This maintains data integrity by backing out changes to the database that were not committed. Only archive logging allows you to roll forward from an earlier version of a DBEnvironment by reapplying all committed transactions up to a specific recovery time. Object A structure created and stored in a DBEnvironment. The most common objects are tables, views, and groups. Owner A DBEUserID, a group name, or a class name. Ownership applies to database objects such as tables, views, indexes, and authorization groups. The owner may drop the object or transfer it to some other owner. Predicate Part of query syntax that specifies a subset of rows to be returned in the query result. Predicates are introduced by the keyword WHERE, so they are sometimes called WHERE clauses. Predicates let you specify a range of values. The comparison predicate lets you compare a column value with a constant or host variable ; the LIKE predicate lets you compare a column value with a portion of a character string; the BETWEEN predicate specifies a range of values for a comparison. Special predicates of various kinds let you search for rows in more complex ways, including the use of subqueries. Preprocessor Converts programs with embedded SQL statements into modified source files for input to a compiler in one of several programming languages: C, COBOL, FORTRAN, and Pascal. Primary Key A column in a table defined so as to permit reference by foreign keys in other tables. A primary key also enforces uniqueness within the column. Procedure A sequence of SQL statements that are stored in a DBEnvironment and applied as a group either through rules or through execution by specific users. Together with rules, procedures let you define generalized constraints within a database to implement the relationships in the database design. Projection Relational operation that extracts a subset of columns from one or more tables. Query Request for information from database tables. A typical example is a SELECT statement. Query Language A set of operators, expressions, and commands that let you manipulate a database. The query language of IMAGE/SQL and ALLBASE/SQL is SQL. Query Result The rows retrieved by a SELECT statement. Query results are also known as result tables. Read Committed (RC) An isolation level that guarantees only that data you read in a transaction has been committed by some earlier transaction; that is, it is not currently in the process of update by some other transaction at the time you are reading it. In practical terms, this means that another transaction can update or delete the same row before your transaction is over. However, concurrency is greatly improved. Read Uncommitted (RU) An isolation level that enforces no separation between your transaction and those of others because no locks are obtained for reads. This level permits dirty reads; that is, reading data from the data buffers that has not and may never be written to the database at all. Referential Integrity An integrity constraint that enforces a relationship between the rows of two tables (a referenced table and a referencing table). Any value you attempt to insert into a table having a referential constraint (a referencing table) must either be NULL or be the same as a value in the referenced table. Relation See Table. Relational Operations Ways of extracting data from relational tables. The three primary relational operations are selection, projection, and joining. Relationship The meaningful interaction of entities in database design. Relationships may be one-to-one, one-to-many, or many-to-many. Repeatable Read (RR) An isolation level that enforces the highest level of separation between the transactions of different users. This level guarantees that when you re-read any data you have read previously in the same transaction, the value seen in the second read will be the same as the value seen in the first read. In practical terms, this means that other users may not update any data you have read at this isolation level until you COMMIT WORK. Result Table See Query Result. Row Horizontal division within a database table. Analogous to a record in a file. Rule A database object that ties the execution of a procedure to specific kinds of data manipulation performed on a database table. Together with procedures, rules let you define generalized constraints within a database to implement the relationships in the database design. Schema A complete SQL database definition. Also, an ISQL command file containing commands to create a DBEnvironment and the objects within it. Also, a TurboIMAGE/XL database definition that is the input to the TurboIMAGE/XL DBSCHEMA program. Selection Relational operation that extracts a subset of rows from one or more tables. Serial Scan A method of reading sequentially from the start of a table until the row is found. Also called table or relation scan. This is the default scan method used to access rows in a table when indexes do not exist. SQL See Structured Query Language. SQLGEN A utility program for database administrators that generates the SQL commands necessary to re-create all or part of a DBEnvironment. The output from SQLGEN is a command file (sometimes called a schema) that can be used as input to ISQL in re-creating database objects. SQLUtil A utility program for database administrators that assists with DBEnvironment maintenance, backup, and recovery. SQLUtil also lets you modify the startup parameters for a DBEnvironment. Structured Query Language A standard query language syntax defined by ANSI standards in the United States and X/OPEN standards in Europe. The relational database query language used by IMAGE/SQL and ALLBASE/SQL. Subquery A query within another query. An example is a subquery embedded in the predicate of another query. The result of the inner query is used to evaluate the outer query. SYSTEM A DBEFileSet created when you issue the START DBE NEW statement. The DBEFile known as DBEFile0 is associated with SYSTEM, which is the DBEFileSet containing the system catalog. You can add DBEFiles to SYSTEM as you would to any other DBEFileSet. Also, a special user associated with the system views in the system catalog. System Catalog A system-maintained database of tables and views owned by the special user SYSTEM and containing information about all the objects in the DBEnvironment. Differs from the DBECon file, which contains startup parameters, not object definitions. System Table See System View. System View A component view within the system catalog. You can issue queries on the views in the system catalog just as you would on ordinary database tables to display information about the DBEnvironment. Table Basic unit of data storage in a relational database. Also known as a relation. Tables consist of rows and columns. A result table is a query result displayed in tabular form. Table Authority Permission to use specific SQL statements on particular tables. There are several kinds of TABLE authority: SELECT, INSERT, DELETE, and UPDATE. SELECT, INSERT, and DELETE let you operate on rows or sets of rows in a table; UPDATE lets you modify specific rows or columns in a table. Transaction A unit of work. Also, a unit of DBEnvironment logging and recovery. A transaction is started with a BEGIN WORK statement and is ended by a COMMIT WORK statement. The BEGIN WORK statement may be implicitly issued by IMAGE/SQL if no other transaction is current when an SQL statement is executed. Unique Constraint An integrity constraint that requires that no two rows in a table have the same values in a specified column or columns. View A table derived by placing a "window" over one or more tables. The derivation of a view is a SELECT statement. View names are governed by the same rules as table names.