Object access method
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Object access method (OAM) is an access method under z/OS which is designed for the storage of large numbers of large files, such as images. It has a number of distinguishing features, e.g. compared to VSAM:
- OAM datasets do not have an internal record structure; they are accessed as binary data streams.
- OAM datasets are not directly cataloged. Rather, they are stored into OAM collections, with only the OAM collection being cataloged. The reason for this is to prevent the catalog from being overloaded with large numbers of (e.g. image) files.
OAM is used in conjunction with DB2. An example use case for OAM would be storing medical images in a DB2 database running under z/OS.
OAM was created in the 1980s "as a prototype product for an insurance company to replace microfiche." Initially OAM supported optical storage and magnetic disks. In the 1990s support for magnetic tape was added. In 2011 support was added for storage of objects in a z/OS unix file system—either zFS or NFS.
- Harding, W. B.; Clark, C. M.; Gallo, C. L.; Tang, H. (1990). "Object storage hierarchy management". IBM Systems Journal. 29 (3): 384–397. ISSN 0018-8670. doi:10.1147/sj.293.0384.
The ability to locate existing objects in storage is fundamental to any data processing system. The facility that carries out the locate function for data sets in an MVS system is the catalog. Typical MVS systems may have tens or even hundreds of thousands of data set entries recorded in a hierarchy of catalogs. In contrast, OAM must be able to manage hundreds of millions of objects, which if individually cataloged would require an excessively large catalog... The system catalog was extended through the concept of collections to handle the large numbers of objects expected for image applications. A catalog entry is defined for each collection, and provides the default storage class and management class assignments for objects stored in the collection, and the identifier of the storage group where the collection is physically stored.
- Vitse, Caroline L. (September 2011). "Reintroducing Object Access Method". IBM Systems Magazine. Retrieved Sep 4, 2014.
- Taylor, Ray H. (1995). "TECHSOURCE: a project to automate the patent operations of the Canadian Intellectual Property Office". World Patent Information. 17 (3): 159–164. ISSN 0172-2190. doi:10.1016/0172-2190(95)00017-T.
The IODM uses data from within its DB2 database tables to determine the location of the documents and retrieves them using the Object Access Method (OAM).
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