Basic Concepts

The root of the 5800 system Java client API is the NameValueObjectArchive class, which represents a connection to a single 5800 system server. All operations are initiated by invoking methods on a NameValueObjectArchive instance after initializing it with the address of a cluster. The fact that a cluster of machines, rather than a single server, is handling the requests is transparent to the application programmer.

A NameValueObjectArchive uses instances of the ObjectIdentifier class to uniquely identify stored data objects. That is, there is a one-to-one correspondence between instances of ObjectIdentifer and 5800 system metadata objects.

There is potentially a many-to-one relationship between metadata and data objects.

When using NameValueObjectArchive, all metadata queries are executed against a 5800 system server’s user-configurable index of name-value pair lists. This class also ensures that a metadata entry is created for every data object stored, even if no metadata is provided at store time.

An instance of the NameValueObjectArchive class functions as a proxy for the 5800 system server. Instantiation incurs some overhead in establishing communication, so reusing a single instance is the recommended practice. Multithreading is supported with the same instance.

NameValueObjectArchive also allows all metadata operations to be performed in terms of two classes that represent metadata records: SystemRecord and NameValueRecord. These classes represent 5800 system metadata entries. When using NameValueObjectArchive, every stored data object has a corresponding NameValueRecord that contains the extended attributes stored with that data object, and each NameValueRecord has a reference to its SystemRecord, which contains built-in system attributes such as data object size and creation time. In this model, all instances of ObjectIdentifer returned from store operations and metadata queries correspond directly to instances of NameValueRecord.

The results of a 5800 system metadata query are returned using instances of the QueryResultSet class, which the application can step through to retrieve metadata or identifiers. This class manages the details of fetching one batch of results after another.