In TurboIMAGE, you start up a database with the following steps:
Create a schema. A common way of doing this is to enter the schema into
a text file created with an editor.
Run DBSCHEMA to generate a root file from the schema.
Run DBUtil to create data sets based on the root file.
The schema contains definitions of all the data items in your database, and it describes all the data sets in the database. It also specifies the required security for the database by defining passwords for specific users.
In ALLBASE/SQL, you start up a DBEnvironment with a simple SQL statement. The statement may be issued interactively (through ISQL), or through an application program. The START DBE NEW statement is as follows:
START DBE 'DBEnvironmentName' NEW
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The START DBE NEW statement creates a file known as a DBECon file, which
is similar to the root file in TurboIMAGE. The DBECon file contains information
about startup parameters for the DBEnvironment and its logs. START DBE NEW also creates a structure within the DBEnvironment known as a system catalog, which is a set of information about all the databases in the DBEnvironment.
Use of a Schema |
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In TurboIMAGE, a schema is required to define a database. Most users create the schema in an ASCII file. Once the database exists, the schema can serve as a record of its contents. The schema can also be used to create the same database structure in different groups and accounts or on different systems.
You can also create a schema for ALLBASE/SQL by entering into an ASCII file all the SQL statements needed to configure the DBEnvironment and create all the objects in it. You can use this file as input to ISQL. However, in ALLBASE/SQL, no schema is required; all that is necessary to configure a DBEnvironment is a START DBE NEW statement issued through ISQL or an application program.
Root File versus DBECon File and System Catalog |
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In TurboIMAGE, the root file, which is generated by DBSCHEMA from the schema, contains security information and definitions of all the data sets in the database, together with the name of the database creator.
The DBECon file in ALLBASE/SQL is created when you issue the START DBE NEW statement. The DBECon file, which has the same name as the DBEnvironment, contains the name of the DBECreator and the names of the logs associated with
the DBEnvironment. It also indicates startup parameters, such as SINGLE or MULTI user mode, and others (examples are shown in the section "Examining Startup Parameters with SQLUtil" in chapter 4).
In ALLBASE/SQL, structural information is also stored internally in a set of system tables known as the system catalog. This is like an internal schema.
The DBECon file does not contain the names of tables or other database objects; these are stored in the system catalog.
Data Files for Data sets versus DBEFiles for Tables |
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Each data set in a TurboIMAGE database occupies a separate MPE/iX file,
created by TurboIMAGE as a PRIV file. The file size is determined from the capacity you indicate for the data set in the schema.
In ALLBASE/SQL, you create a table inside a DBEFileSet, to which you have added one or more DBEFiles. These DBEFiles need to be large enough for the amount of data you need to store. Instead of specifying a capacity, you create DBEFiles of whatever size is needed. DBEFiles can hold data and/or indexes for more than one table at a time; no simple correspondence between tables and data files exists. You do not specify the size of a table when you create it; the table size is limited only by the capacity of your system. As you need additional space for a growing table, you add DBEFiles to the DBEFileSet in which the table was created. This increases the capacity of the table. (An exception to this is tables created as hash structures, described in a later section.)
Naming Conventions |
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The names of data items and data sets within a TurboIMAGE schema may contain some characters which are not allowed in ALLBASE/SQL. For example, the hyphen is not allowed in ALLBASE/SQL names; so hyphens need to be represented in some other way in ALLBASE/SQL, for example, by an underscore (_).
