Forward Index

Introduction

The Forward Index is responsible for the capability of storing and retrieving key and value pairs. The values can be retrieved by indicating an interval for the keys. The Forward Index Service design pattern is similar/the same as to the Full Text Index Service design and the Geo Index Service design.

Implementation Overview

Services

The forward index is implemented through three services. They are all implemented according to the factory-instance pattern:

• An instance of ForwardIndexManagement Service represents an index and manages this index. The life-cycle of the index is the same as the life-cycle of the management instance; the index is created when the ForwardIndexManagement instance is created, and the index is terminated (deleted) when the ForwardIndexManagement instance resource is removed. The ForwardIndexManagement Service manage the life-cycle and properties of the forward index. It co-operates with instances of the ForwardIndexUpdater Service when feeding content into the index, and with instances of the ForwardIndexLookup Service for getting content from the index. The Content Management service is used for safe storage of an index. A logical file is established in Content Management when the index is created. The index is retrieved from Content Management and established on the local node when an existing forward index is dynamically deployed on a node. The logical file in Content Management is deleted when the ForwardIndexManagement instance is deleted.
• The ForwardIndexUpdater Service is responsible for feeding content into the forward index. The content of the forward index consists of key value pairs. A ForwardIndexUpdater Service resource updates a single Index. One index may be updated by seveal ForwardIndexUpdater Service instances simultaneously. When feeding the index, a ForwardIndexUpdater Service is created, with the EPR of the FullTextIndexManagement resource connected to the Index to update. The ForwardIndexUpdater instance is connected to a ResultSet that contains the content to be fed to the Index.
• The ForwardIndexLookup Service is responsible receiving queries for the index, and returning responses that matches the queries. The ForwardIndexLookup gets a reference to the ForwardIndexManagement instance that is managing the index, when it is created. It can only query this index. Several ForwardIndexLookup instances may query the same index. The ForwardIndexLookup instances gets the index from Content Management, and establishes a local copy of the index on the file system that is queried. The local copy is kept up to date by subscribing for index change notifications that are emitted my the ForwardIndexManagement instance.

It is important to note that none of the three services have to reside on the same node; they are only connected through WebService calls and the DILIGENT CMS. The following illustration shows the information flow and responsibilities for the different services used to implement the Full Text Index:

(illustration will be improved shortly... )

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RowSet

The content to be fed into an Index, must be served as a ResultSet containing XML documents conforming to the ROWSET schema. This is a simple schema, contaning key and value pairs. The following is an example of a ROWSET for that can be fed into the Forward Index Updater: