A |
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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).
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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.
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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.
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ATCUtil | |
Another name for the IMAGE/SQL utility program.
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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.
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Authority | |
Permission to access specific objects for specific purposes
within a DBEnvironment.
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Authorization Group | |
See Group.
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B |
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Base Table | |
Table upon which a view is based.
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C |
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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.
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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.
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Column | |
Vertical division within a database table. Analogous to an
item in a TurboIMAGE/XL dataset.
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Column Authorization | |
Permission to update a specific column within a table.
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Column List | |
One or more columns specified as part of a query result.
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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.
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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.
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D |
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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.
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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.
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Data Manipulation | |
The process of accessing data within a database.
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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.
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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 “Moving from TurboIMAGE/XL to IMAGE/SQL” for a maping of these SQL data types to TurboIMAGE
data types.
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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.
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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.
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Database Design | |
The creation of a specific arrangement of data in tables
or data sets with an appropriate security structure.
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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.
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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.
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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.
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DBECreator | |
The individual who issues the START DBE NEW statement. See DBC.
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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.
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DBEFileSets | |
Logical grouping of DBEFiles.
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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.
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DBEUserID | |
A login name and account name joined
with the character '@'. One type of owner of database objects.
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E |
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Embedded SQL Programming | |
An application program incorporating SQL statements for programmatic
access to IMAGE/SQL databases.
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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.
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Explicit Locking | |
Locking of tables in transactions by the use of the LOCK TABLE statement.
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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.
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G |
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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.
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I |
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IMAGE/SQL Database | |
A TurboIMAGE/XL database attached to an SQL DBEnvironment.
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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.
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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 .
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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.
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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.
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J |
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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.
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K |
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Key | |
One or more columns on which an index, hash structure, or integrity
constraint are based.
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L |
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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.
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Logging | |
The use of log files to record operations that modify database files.
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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.
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O |
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Object | |
A structure created and stored in a DBEnvironment. The most
common objects are tables, views, and groups.
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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.
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P |
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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.
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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.
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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.
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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.
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Projection | |
Relational operation that extracts a subset of columns from
one or more tables.
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Q |
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Query | |
Request for information from database tables. A typical example is
a SELECT statement.
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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.
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Query Result | |
The rows retrieved by a SELECT statement. Query results are also known
as result tables.
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R |
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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.
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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.
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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.
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Relation | |
See Table.
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Relational Operations | |
Ways of extracting data from relational tables. The three primary
relational operations are selection, projection, and joining.
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Relationship | |
The meaningful interaction of entities in database design. Relationships
may be one-to-one, one-to-many, or many-to-many.
|
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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.
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Result Table | |
See Query Result.
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Row | |
Horizontal division within a database table. Analogous to a record
in a file.
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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.
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S |
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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.
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Selection | |
Relational operation that extracts a subset of rows from one
or more tables.
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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.
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SQL | |
See Structured Query Language.
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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.
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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.
|
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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.
|
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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.
|
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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.
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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.
|
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System Table | |
See System View.
|
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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.
|
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T |
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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.
|
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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.
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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.
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U |
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Unique Constraint | |
An integrity constraint that requires that no two rows in a table have the
same values in a specified column or columns.
|
---|
V |
---|
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.
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