To query or update data in a sequential file, you must create a
relational table that maps to that file. You can also create a view on the
table to filter record types or filter rows and columns. You use the New
Sequential Table wizard to create the table and optionally the
view.
Restrictions
- Sequential data sets cannot be updated.
- Because sequential data sets do not have any native index definitions
or keys, any request to access a sequential data set causes a table scan.
You cannot use Data Architect to create indexes for tables that are mapped
to sequential data sets.
- If you are mapping partitioned sequential data sets, a table must map
to a single member within a partitioned data set.
- SQL access to extended partitioned data sets is not supported.
- When a table references a direct access data set, these data sets are
referred to as BDAM (Basic Direct Access Method) data sets. BDAM data sets
can be accessed using “keys” that consist of track addresses, block numbers,
or a combination of the two. Classic Data Architect does not access a direct
access data set using any of these techniques, but Classic Data Architect
can sequentially retrieve the records that are stored in one of these direct
access data sets.
About this task
Classic
federation uses two methods to physically access a sequential file:
- The table definition can refer to the data set name. This method requires
the data server to issue dynamic allocation requests before the file is physically
opened. For Classic Federation to use dynamic allocation, the file must be
cataloged.
- The table definition can reference the file by DD (statement) name. Accessing
the file by DD name requires that the file is statically and permanently allocated
to the server address space because the referenced DD statement must be added
to the server JCL, and the DSN parameter on the DD statement identifies the
physical file to be accessed.
The recommended technique is to use dynamic allocation to access
a sequential file. When a file is dynamically allocated, the file disposition
is share mode, which allows other applications to access the file concurrently,
if the applications are not attempting to access the file in exclusive mode.
For
more information about creating tables and views that map to sequential files,
see the related links for sequential syntax diagrams and for views.
Procedure
To create a sequential table and optionally a view
for Classic federation: