Accessing VSAM and AS/400 Files

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Most enterprise data is still stored in VSAM files. A useful data access technology must provide a way to access this information and make it available over the intranet as well as the Internet. Some reasons why you might want this capability include:

  • Web access to VSAM files.
  • Decision-support systems with fast record and file downloads.
  • Windows NT-to-mainframe backups.
  • Bulk data copy from VSAM to SQL Server.
  • Mainframe-based data with server-based business rules.

If your application requires data access to VSAM or AS/400 file systems, you can use the SNA Server OLEDB/DDM provider to directly access record-oriented files in place on the mainframe. This approach preserves the storage, management, backup, and security provided by the original mainframe system.

The OLEDB/DDM provider is an OLE DB data provider for IBM's Distributed Data Management (DDM) architecture. The OLEDB/DDM provider accesses by file, record, or stream I/O. The stream I/O interface is especially useful for accessing entire files or data set members at one time. The stream I/O interface accesses VSAM data set members as though they were files on a Windows NT Server local drive. This results in fast data transfers.

The OLEDB/DDM provider uses the record-level input/output (RLIO) protocol of the IBM Distributed Data Management (DDM Architecture Level 2 and higher) system. The driver is implemented as a source DDM requester and interacts with target DDM server implementations on most popular mainframe environments, including MVS/ESA, OS/390, and AS/400.

Because the OLEDB/DDM provider is an OLE DB data provider, it provides access to many different mainframe file types. A single application could use the same OLEDB/DDM technology to access many different files types, including the following:

  • VSAM
  • DB2
  • IMS
  • AS/400

Choosing OLEDB/DDM Instead of ODBC/DRDA

Many large enterprise data centers have implemented ODBC-to-Distributed Relational Database Architecture (DRDA). Unfortunately, ODBC/DRDA drivers require all access requests to be structured as SQL statements, which are then interpreted by the mainframe DB2 and AS/400 object file systems. To process an SQL SELECT statement, the SQL engine in DB2 or the AS/400 file system accesses an index of the target physical file using a logical file called a "view." For the majority of mainframe-based data, no SQL view files are associated with the physical data files. Without the ability to read the mainframe application–created logical file, ODBC/DRDA requests must be processed by continually scanning the data file until the requested record is found.

Unlike ODBC/DRDA drivers, the OLEDB/DDM provider offers record-level I/O access, which is a faster and more flexible method of accessing mainframe-based data than the DRDA approach. The majority of data files on mainframes and AS/400s are not designed to handle SQL, but instead are indexed by COBOL and RPG applications to allow access through a logical file created by the mainframe application. The IBM DDM RLIO protocol allows any DDM-compliant application to access these logical files, providing fast access to record-level data in all VSAM and all AS/400 files. OLEDB/DDM outperforms ODBC/DRDA drivers because it provides a more direct route to the target data.

Working with Distributed Data Management

From a Windows–based distributed application point of view, IBM's Distributed Data Management (DDM) server software is a good way to access non-relational mainframe data — especially for ad hoc, read-only, or non-transactional access. IBM DDM servers are available and running on the most popular mainframe operating systems, including MVS and AS/400. To provide the easiest and most efficient access to files running on MVS and the AS/400, SNA Server uses OLE DB to provide a complete and single solution to access multiple file types on multiple platforms. The Microsoft OLE DB Provider for AS/400 and VSAM supports DFSMS version 2 release 1 or later for MVS/ESA and OS/390. Additionally, AS/400 V2R2 or later is a compliant DDM Server.

The OLEDB/DDM provider requires no mainframe application source code changes. Data can be accessed on both AS/400 and MVS VSAM data sets. The native record-level I/O interface, as defined by the DDM architecture, is used for optimal performance and ease of implementation. You can integrate non-SQL, non-relational information with SQL and relational data stores without first migrating the data files to a Windows NT Server platform.

This VSAM connectivity supports both fixed and variable logical record length classes, full data set browsing, file and record locking, and file and record attribute preservation.

The OLEDB/DDM provider supports both fixed and variable logical record lengths, full data set browsing, file and record locking, and file and record attribute preservation.

Supported AS/400 file types include:

  • Physical file with external record description.
  • Logical file with external record description.

Supported mainframe data set types include:

  • Sequential access method file (SAM).
  • Entry-Sequenced Data Set (ESDS).
  • Key-Sequenced Data Set (KSDS).
  • Relative Record Data Set (RRDS).
  • Alternate index for ESDS and KSDS data sets (AltIdx).
  • Partitioned Data Set (PDS) members.
  • Partitioned Data Set extended members (PDSE).