This section provides an overview of 5800 system semantics.
The 5800 system stores two types of data: arbitrary object data and structured metadata records. Every metadata record is associated with exactly one data object. Every data object has at least one metadata record. A unique object identifier (OID) is returned when a metadata record is stored. The OID can later be used to retrieve the metadata record or its object data. In addition, metadata records can be retrieved by a query:
OID ↔ Metadata Record -> Object Data
The two types of metadata are system metadata and user metadata. The names and types of system metadata are predefined and cannot be overridden by the user.
A user metadata record consists of a set of attributes. The set of possible attributes is defined by the schema. Only one schema exists for each 5800 system. For information on configuring a schema, see “Configuring Metadata and File System Views” in Sun StorageTek 5800 System Administration Guide.
The 5800 system emulator loads its schema from an XML file. The metadata_merge_config utility can be used to extend the default schema, appending the new entries to the original schema, which is then read by the emulator. For additional information, see Chapter 2, Example Applications and Chapter 3, Sun StorageTek 5800 System Emulator.
For information on the valid data types that you can use when specifying attributes in a schema, see “Configuring Metadata and File System Views” in Sun StorageTek 5800 System Administration Guide.
A namespace is a container that holds a set of typed attribute names. Attribute names must be unique within a given namespace. Defining a namespace is a way to organize and group together a set of related attribute names for a given application. For more information, see “Configuring Metadata and File System Views” in Sun StorageTek 5800 System Administration Guide