Last Modified: 3-Nov-1998
Reviewed: 29-Oct-1998

Transient Data Store

Purpose and Functionality

The Transient Data Store is a passive component of the architecture where transient representations of data objects are stored temporarily during the execution of the algorithms. It is the "logical" place where these data objects are stored. In particular, they can be in any place in memory space but logically are in the transient store. Various transient data stores are foreseen in one application characterized by the lifetime and nature of the contained data. For example, there are the Transient Event Data Store,  Transient Detector Data Store and Transient Histogram Data Store.

The Transient Event Data Store is managed by the EventDataSvc. This service implements the interface for accessing the data by any client and in particular by the Algorithms. The clients need to know how the data is organized, identified and ownership conventions.

• Data Organization. The data in the data store is organized in a strong hierarchical tree structure. All data objects are logically connected to one an only one container. Containers are also connected to one and only one container. This stucture resembles very closely a file system with directories.
• Data Identification. All data objects in the data store need to be identified easily. The identification should be based on logical names and not physical addresses. The identification follows the data organization. That is, the full identification of an object is the concatenation of the identification of the container which contains the object and the identification of the object inside the container (equivalence of the filename and full path in file systems).
• Data ownership. The data objects in the data store are owned by the data service that is managing the store. The clients registering data objects in the store lose their ownership. This means that they are not allowed to delete the objects, change essential characteristics like the identification, etc... References to objects in the data store are not valid after the lifetime of the data. For example, references to event data objects are not valid after the current event has been process and a new one has been loaded.

Interfaces

The Transient Data Store do not offer any interface directly to clients. The interface is implemented by the corresponding Data Service. Clients of the Transient Data Store are allowed to keep direct references to objects in the store as long as the validity period and ownership conventions are obeyed.

Dependencies

Since the Transient Data Store is a passive component it does not need any other component of the system to perform its function (storing data objects is memory).