Version 4.2.6 for Mainframes
 —  Database Management System Interfaces  —

DDM Generation

This section covers the following topics:


Natural Data Definition Module - DDM

To enable Natural to access an SQL table, a logical Natural data definition module (DDM) of the table must be generated. This is done either with Predict (see the relevant Predict documentation for details) or with the Natural utility SYSDDM.

If you do not have Predict installed, use the SYSDDM function SQL Services to generate Natural DDMs from SQL tables. This function is invoked from the main menu of SYSDDM and is described on the following pages.

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SQL Services (NSB)

To access SQL tables, you may use the SQL Services (NSB) function of the Natural SYSDDM utility; see Function Code Z in the section Description of Functions in the Natural Editors documentation. You access the CXX CDD (ConnecX data dictionary) of your current CXX connection to retrieve table definitions for Natural DDM generation. The name of the CDD catalog you access is displayed in the top left-hand corner of the screen SQL Services Menu. You can access any catalog contained in the CDD. For further details on the CDD structure read the ConnecX documentation.

Start of instruction setTo invoke the SQL Services (NSB) function

  1. In the command line, enter the Natural system command SYSDDM.

    The menu of the SYSDDM utility appears.

  2. In the Code field, enter function code Z.

    A menu is displayed, which offers you the following functions:

These Functions are described in the following sections.

Select Catalog Name from a List

This function is used to select a catalog from the catalogs defined in the CDD for further processing.

To invoke this function, enter function code C on the SQL Services Menu.

If you enter the function only, you obtain a list of all catalogs defined in the current CDD.

On the list, you can mark an SQL catalog with S to select a catalog for further processing.

The selected catalog is displayed in the left corner of the second header line of following maps and in the Catalog name field of the SQL Services Menu, where the catalog name could also be entered. If you did not explicitly specify a catalog name it is set to either the current default catalog of the CXX connection – if it is not equal spaces- or the first catalog found in the current CDD.

CXX Connection Handling

This function is used to verify the actual CXX connection. It displays the current parameters of the actual connection. These parameters are:

Parameter Description
GATEWAY Specifies the IP-address of the CXX server connected to.
DD Specifies the registered data source name of the CDD in use.
PORT Specifies the port number the CXX server is listening to.
User Specifies the user name of the CXX connection.
Password Specifies the password used for the CXX connection(invisible).
Catalog Specifies the current default catalog name of the CXX connection.
Schema Specifies the current default schema name of the CXX connection.
Version Displays the RCI version string of the CXX connection.
State Displays the CXX connection state.

To invoke this function, enter function code X on the SQL Services Menu.

The parameters of the connection could be changed and the connection could be (re-)established with the entered parameters by pressing PF5 (Update).

Select SQL Table from a List

This function is used to select an SQL table from a list for further processing.

To invoke the function, enter function code S on the SQL Services Menu.

If you enter the function code only, you obtain a list of all tables defined in the selected SQL catalog.

If you do not want a list of all tables but would like only a certain range of tables to be listed, you can, in addition to the function code, specify a start value in the Table Name and/or Schema fields. You can also use asterisk notation (*) for the start value.

When you invoke the function, the Select SQL Table from a List screen is invoked displaying a list of all SQL tables requested.

On the list, you can mark an SQL table with either G for Generate DDM from an SQL table or L for List Columns of an SQL table. Then the corresponding function is invoked for the marked table.

Generate DDM from an SQL Table

This function is used to generate a Natural DDM from an SQL table, based on the definitions in the SQL catalog.

To invoke the function, enter function code G on the SQL Services Menu along with the name and creator of the table for which you wish a DDM to be generated.

If you do not know the table name/schema, you can use the function Select SQL Table from a list to choose the table you want.

If you do not want the schema name of the table to be part of the DDM name, enter an N in the field DDM Name with Creator when you invoke the Generate function (default is Y).

Important:
Since the specification of any special characters as part of a field or DDM name does not comply with Natural naming conventions, any special characters allowed within SQL must be avoided. SQL delimited identifiers must be avoided, too.

If you wish to generate a DDM for a table for which a DDM already exists and you want the existing one to be replaced by the newly generated one, enter a Y in the Replace field when you invoke the Generate function.

By default, Replace is set to N to prevent an existing DDM from being replaced accidentally. If Replace is N, you cannot generate another DDM for a table for which a DDM has already been generated.

DBID/FNR Assignment

When the function Generate DDM from an SQL Table is invoked for a table for which a DDM is to be generated for the first time, the DBID/FNR Assignment screen is displayed. If a DDM is to be generated for a table for which a DDM already exists, the existing DBID and FNR are used and the DBID/FNR Assignment screen is suppressed.

On the DBID/FNR Assignment screen, enter one of the database IDs (DBIDs) chosen at Natural installation time, and the file number (FNR) to be assigned to the DB2 table. Natural requires these specifications for identification purposes only.

The range of DBIDs which is reserved for SQL tables is specified in the NTDB parameter macro of the Natural parameter module (see the Natural Parameter Reference documentation) in combination with the NDBID macro of the parameter module NDBPARM. Any DBID not within this range is not accepted. The FNR can be any valid file number within the database (between 1 and 255).

Long Field Redefinition

The maximum field length supported by CXX is 32 KB - 1. If an SQL table contains a column which is longer than 253 bytes, the pop-up window Long Field Generation will appear automatically.

A field which is longer than 253 bytes may be defined as a simple Natural field with a maximum length of 32 KB -1, or as an array. In the DDM, such an array is represented as a multiple-value variable.

If, for example, a DB2 column has a length of 2000 bytes, you can specify an array element length of 200 bytes, and you receive a multiple-value field with 10 occurrences, each occurrence with a length of 200 bytes.

Since redefined long fields are not multiple-value fields in the sense of Natural, the Natural C* notation makes no sense here and is therefore not supported.

When such a redefined long field is defined in a Natural view to be referenced by Natural SQL statements (that is, by host variables which represent multiple-value fields), both when defined and when referenced, the specified range of occurrences (index range) must always start with occurrence 1. If not, a Natural syntax error is returned.

Example:

UPDATE table SET varchar = #arr(*)
SELECT ... INTO #arr(1:5)

Note:
When such a redefined long field is updated with the Natural DML UPDATE statement (see the relevant section in the Statements documentation), care must be taken to update each occurrence appropriately.

Length Indicator for Variable Length Fields: VARCHAR, LONG VARCHAR, VARGRAPHIC, LONG VARGRAPHIC

For each of the columns listed above, an additional length indicator field (format/length I2) is generated in the DDM. The length is always measured in number of characters, not in bytes. To obtain the number of bytes of a VARGRAPHIC or LONG VARGRAPHIC field, the length must be multiplied by 2.

The name of a length indicator field begins with L@ followed by the name of the corresponding field. The value of the length indicator field can be checked or updated by a Natural program.

If the length indicator field is not part of the Natural view and if the corresponding field is a redefined long field, the length of this field with UPDATE and STORE operations is calculated without trailing blanks.

Null Values

With Natural, it is possible to distinguish between a null value and the actual value zero (0) or blank in an SQL column.

When a Natural DDM is generated from the SQL catalog, an additional NULL indicator field is generated for each column which can be NULL; that is, which has neither NOT NULL nor NOT NULL WITH DEFAULT specified.

The name of the NULL indicator field begins with N@ followed by the name of the corresponding field.

When the column is read from the database, the corresponding indicator field contains either zero (0) (if the column contains a value, including the value 0 or blank) or -1 (if the column contains no value).

Example:

The column NULLCOL CHAR(6) in an SQL table definition would result in the following view fields:

NULLCOL  A 6.0 
N@NULLCOL  I 2.0 

When the field NULLCOL is read from the database, the additional field N@NULLCOL contains:

A null value can be stored in a database field by entering -1 as input for the corresponding NULL indicator field.

Note:
If a column is NULL, an implicit RESET is performed on the corresponding Natural field.

List Columns of an SQL Table

This function lists all columns of a specific SQL table.

To invoke this function, enter Function Code L on the SQL Services Menu along with the name and creator of the table whose columns you wish to be listed.

The List Columns screen for this table is invoked, which lists all columns of the specified table and displays the following information for each column:

Variable

Content

Name

The name of the column.

Type

The column type.

Length

The length (or precision if Type is DECIMAL) of the column as defined in the DB2 catalog.

Scale

The decimal scale of the column (only applicable if Type is DECIMAL).

Update

Y - The column can be updated.

N - The column cannot be updated.

Nulls

Y - The column can contain null values.

N - The column cannot contain null values.

Not

A column which is of a scale length or type not supported by Natural is marked with an asterisk (*). For such a column, a view field cannot be generated. The maximum scale length supported is 7 bytes.

Types supported are:

CHAR, VARCHAR, LONG VARCHAR, GRAPHIC, VARGRAPHIC, LONG VARGRAPHIC, DECIMAL, INTEGER, SMALLINT, DATE, TIME, TIMESTAMP, FLOAT, ROWID, BLOB, CLOB and DBCLOB.

The data types DATE, TIME, TIMESTAMP, FLOAT and ROWID are converted into numeric or alphanumeric fields of various lengths: DATE is converted into A10, TIME into A8, TIMESTAMP into A26, FLOAT into F8 and ROWID into A40.

When you invoke the function, the Select SQL Table from a List screen is invoked displaying a list of all SQL tables requested.

For SQL, Natural provides an SQL TIMESTAMP column as an alphanumeric field (A26) in the format YYYY-MM-DD-HH.SS.MMMMMM.

Since Natural does not yet support computations with such fields, a Natural subprogram called NDBSTMP is provided to enable this kind of functionality.

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