OSF DCE Application Development Guide--Core Components

Chapter 5. The DCE Backing Store

This chapter describes the backing store library that DCE provides for the convenience

of programmers who are writing DCE servers. A backing store is a persistent database

or persistent object store from which typed data can be stored and retrieved by a key.

Note: Sometimes the backing store is called a database. For instance, the

associated IDL ﬁle is dce/database.idl, and the name of the backing store

routines begin with dce_db_. The backing store is, however, not a full-

ﬂedged database in the conventional sense, and it has no support for SQL

or for any other query system.

Servers generally need to manage several objects. Good design often requires that the

state of the objects be maintained over sequential instances of a particular server. For

example, the ACLs used by a server should not need to be recalculated each time the

system is rebooted. The backing store interface provides a way to store, into a ﬁle, any

data that can be described with IDL so that it can persist across instances of software that

run from time to time. For example, the ACL library uses the backing store library. The

backing store routines can be used in servers, in clients or in standalone programs that do

not involve remote procedure calls (RPCs). Backing store data should not be used for

sharing data between processes.

5.1 Data in a Backing Store

The backing store interface provides the applications programmer with the capability for

tagged storage and retrieval of typed data. The tag (or retrieval key) can be either a

UUID or a standard C string. For a speciﬁc backing store, the data type must be

speciﬁed at compile time and is established through the IDL encoding services. Each

backing store can contain only a single data type.

Each data item (which may also be called a data object,oradata record) consists of the

data stored in a single call to a storage routine. The storage routines are dce_db_store(),

dce_db_store_by_name(), and dce_db_store_by_uuid( ). Optionally, data items may

have standard headers. If a backing store has been created to use headers, then every

data item has the header.

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