VSAM data sets can be defined with either the DEFINE CLUSTER command or the ALLOCATE command. When a cluster is defined, VSAM uses the following catalog entries to describe the cluster:

• A cluster entry describes the cluster as a single component.
• A data entry describes the cluster's data component.
• For a key-sequenced data set, an index entry describes the cluster's index component.

All of the cluster's attributes are recorded in the catalog. The information that is stored in the catalog provides the details needed to manage the data set and to access the VSAM cluster or the individual components.

If you use DEFINE CLUSTER, attributes of the data and index components can be specified separately from attributes of the cluster.

• If attributes are specified for the cluster and not the data and index components, the attributes of the cluster (except for password and USVR security attributes) apply to the components.
• If an attribute that applies to the data or index component is specified for both the cluster and the component, the component specification overrides the cluster's specification.