This section covers the following topics:
With a few exceptions Natural provides all of the functionality of third generation language programming in the DL/I environment.
However, accessing DL/I data using Natural is significantly different from programming techniques used in a third generation language. Natural application programmers do not have to code specific DL/I calls or build the segment search arguments (SSAs). They do not need to concern themselves with PCB mask information or keep track of PCB positioning between Syncpoints.
Natural for DL/I operates as a standard DL/I application and although most of the DL/I call processing is done internally, it is important to realize that all of the required DL/I processing is still performed:
PSBs are scheduled and terminated, PCBs are selected for use, database
positioning is maintained, SSAs are created, the most efficient DL/I calls are
issued, PCB mask information is evaluated, GET HOLD
calls are issued before update or delete operations.
These tasks are all being performed for the application by Natural.
It is important to note that Natural is performing these tasks based on
the information available in the application program. If, for example, a
READ or FIND statement in a program is lacking
essential segment search information, Natural selects a PCB, builds an SSA and
issues a certain DL/I call based on this lacking information.
The Natural programmers use the same Natural statements to manipulate data in DL/I as they would for VSAM, Adabas or DB2.
Natural accesses DL/I segments based on the Natural DDM which is being referenced. Since the data access is always for one specific segment type (the one defined by the DDM), Natural neither issues path calls nor unqualified calls; that is, calls where the segment name is not specified.
Anmerkungen:
LOG, STAT
and GSCD call functions are not supported for the
IMS TM environment.
This section mainly consists of information also contained in the Natural Statements documentation, where each Natural statement is described in detail, including notes on DL/I usage where applicable. Summarized below are the particular points a programmer has to bear in mind when using Natural statements with DL/I.
Any Natural statement not mentioned in this section can be used without restrictions with DL/I.
The Natural statement BACKOUT
TRANSACTION is used to back out all database updates
performed during the current logical transaction.
How the statement is translated and which command is actually issued depends on the TP-monitor environment:
Under CICS, the BACKOUT TRANSACTION statement is
translated into an EXEC CICS ROLLBACK command.
However, in pseudo-conversational mode (PSEUDO=ON), only changes
made to the database since the last terminal I/O are undone. This is due to
CICS-specific transaction processing.
In batch mode and under IMS TM, Natural for DL/I issues
ROLB calls without checking the
CMPAT setting in the corresponding NSB. However, under
IMS TM, only changes made to the database since the last terminal I/O are
undone. This is due to IMS TM-specific transaction processing.
Because PSB scheduling is terminated by a Syncpoint/checkpoint request,
Natural saves the PCB position before executing the BACKOUT
TRANSACTION statement. Before the next command execution, Natural
reschedules the PSB and tries to set the PCB position as it was before the
backout.
Anmerkung:
The PCB position might be shifted forward if any pointed segment
had been deleted in the time period between the BACKOUT
TRANSACTION and the following statement.
The Natural statement DELETE is used to delete a
segment from a DL/I database, which also deletes all descendants of the
segment.
The DL/I AIX fields can be displayed with the Natural statement
DISPLAY only if a PCB
is used with the AIX specified in the parameter PROCSEQ.
If not, an error message is returned by Natural for DL/I at runtime.
The Natural statement END
TRANSACTION indicates the end of a logical transaction and
releases all DL/I data locked during the transaction. All data modifications
are committed and made permanent.
How the statement is translated and which command is actually issued depends on the TP-monitor environment:
Under CICS, the END TRANSACTION statement is translated
into an EXEC CICS SYNCPOINT command.
In batch mode and non-message-driven BMP environments, Natural for
DL/I issues CHKP calls without checking the
CMPAT setting in the corresponding NSB.
In MPP and message-driven BMP environments, the END
TRANSACTION statement is not translated into a
CHKP call, but is ignored, because
CHKP calls imply GU calls. As Natural is a
conversational transaction, you must reply to the terminal before requesting
the next message (that is, before issuing the next
GU call). An implicit end-of-transaction is issued
after each terminal I/O.
Because PSB scheduling is terminated by a
SYNCPOINT/CHECKPOINT
request, Natural saves the PCB position before executing the END
TRANSACTION statement. Before the next command execution, Natural
reschedules the PSB and tries to set the PCB position as it was before the
END TRANSACTION statement.
Anmerkung:
The PCB position might be shifted forward if any pointed segment
had been deleted in the time period between the END TRANSACTION
and the following command.
With batch-oriented BMP regions, user data can be checkpointed on the
IMS system log data sets. This is done by supplying an 8-byte checkpoint ID as
the first operand in the END TRANSACTION statement, and by
specifying the areas to be checkpointed as additional operands.
If the database specified with the Natural profile parameter
ETDB is not
the same as the database affected by the transaction, the first operand of the
END TRANSACTION statement will be used as checkpoint ID for the
ETDB database, while NATDLICK will be used as checkpoint ID for
the other database not specified with the
ETDB
parameter.
The total area to be checkpointed must not exceed 1992 bytes; see also Symbolic Checkpoint/Restart Functions.
With DL/I, the Natural FIND statement is typically used
when a specific search criterion is known and specific segments are to be
retrieved. This issues a DL/I GET UNIQUE call.
However, if the FIND statement specifies a lower level segment and
is within an active READ
or FIND loop for an ancestor segment, it generally results in a
DL/I GET NEXT WITHIN PARENT call.
The FIND statement initiates loop processing, which is
active until all segment occurrences which match the search criterion have been
read.
When accessing a field starting after the last byte of the given segment occurrence, the storage copy of this field is filled according to its format (numeric, blank, etc.).
FIND
FIRST, FIND
NUMBER and FIND UNIQUE are not
permitted. The PASSWORD,
CIPHER,
COUPLED
and RETAIN
clauses are not permitted either.
In the WITH clause, you can
only use descriptors that are defined as key fields in DL/I and marked with
"D" in the DDM.
When connecting search criteria, the following has to be observed:
[NOT]
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basic-search-criterion |
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search-expression |
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Connecting search criteria for segment type A results in multiple qualification statements within one DL/I segment search argument (SSA). Connecting search criteria for segment types A and B results in multiple SSAs. Therefore, the Boolean operator OR cannot be used to combine search criteria for different segment types.
The Natural statement GET
TRANSACTION DATA retrieves checkpoint data saved by an
END
TRANSACTION statement. The first parameter of this statement
must be an 8-byte checkpoint ID. The remaining operands must be listed in the
same sequence, length and format as in the corresponding END
TRANSACTION statement; see also
Symbolic
Checkpoint/Restart Functions.
The Natural statement READ should be used to process a
set of segment occurrences in sequential order and usually results in a DL/I
GET NEXT call.
When the READ statement is used, segments are retrieved
based on the sequence field of the root segment or based on a secondary index
field. Since the READ statement initiates sequential access of the
database, it is important to understand that the EQUAL
TO clause means the same thing as the STARTING FROM clause;
it initiates a sequential read loop beginning with the key value specified.
The READ statement initiates loop processing. A loop is
active until all segment occurrences which match the search criterion have been
read.
The PASSWORD and CIPHER clauses are not
permitted.
IN PHYSICAL
SEQUENCE is used to read records in the order in which they
are physically stored in a database. The physical sequence is the default
sequence.
Anmerkung:
This is only valid when using Natural with HDAM databases.
BY ISN is
not valid when using Natural with DL/I.
For Natural, the descriptor used must be either the sequence field of
the root segment or a secondary index field. If a secondary index field is
specified, it must also be specified in the PROCSEQ
parameter of a PCB. Natural uses this PCB and the corresponding hierarchical
structure to process the database.
The Natural statement RELEASE is not applicable for
DL/I usage, since it releases sets of records retained by a
FIND statement that
contained a RETAIN clause, which
is not valid when using Natural with DL/I.
The Natural statement STORE can be used to add a
segment occurrence.
If the segment occurrence is defined with a primary key, a value for the primary key field must be provided.
In the case of a GSAM database, records must be added at the end of the database (due to GSAM restrictions).
The USING/GIVING
NUMBER clause is not valid when using Natural with DL/I.
If the SET/WITH clause
is used, the following applies with Natural for DL/I:
Values must be provided for the segment sequence field and for all sequence fields of the ancestors.
Only I/O (sensitive) fields can be provided.
A segment of variable length is stored with the minimum length
necessary to contain all fields as specified with the STORE
statement. The segment length will never be less than the minimum size
specified in the SEGM macro of the DBD.
If a multiple-value field or a periodic group is defined as variable
in length, at the end of the segment only the occurrences as specified in the
STORE statement are written to the segment and define the segment
length.
The Natural statement UPDATE can be used to update a
segment in a DL/I database. The segment length is increased (if necessary) to
accommodate all fields specified with the UPDATE statement. If a
multiple-value field or a periodic group is defined as variable in length, only
the occurrences as specified in the UPDATE statement are written
to the segment.
The DL/I AIX field name cannot be used in an UPDATE
statement. AIX fields, however, can be updated by referring to the source field
which comprises the AIX field.
DL/I sequence fields cannot be updated because of DL/I restrictions.
If the SET/WITH clause
is used, only I/O (sensitive) fields can be provided. A segment sequence field
cannot be updated (DELETE and
STORE must be used
instead).
Due to GSAM restrictions, the UPDATE statement cannot be
used for GSAM databases.
With the Natural statement WRITE, the DL/I AIX fields can be
displayed only if a PCB is used with the AIX specified in the parameter
PROCSEQ. If not, an error message is returned by Natural
for DL/I at runtime.
The following Natural statements are not available for DL/I users:
With DL/I, the following restrictions apply to the following Natural system variables:
As there is no DL/I equivalent to Adabas internal sequence numbers
(ISNs), the system variable *ISN is not
available with Natural for DL/I.
With Natural for DL/I, the Natural system variable
*NUMBER
does not contain the number of segment occurrences found. It contains
0 if no segment occurrence satisfies the search criterion and a
value of 8,388,607=X'7FFFFF' if at least one segment occurrence
satisfies the search criterion.
