Access Support Tree and TextArray: a data structure for XML document storage and retrieval

Abstract

The characteristics of XML documents require new ways of storing and querying such documents. Queries on both textual content and structural aspects must be supported efficiently. For this reason, we examined existing work on both document storage approaches and models for querying documents to derive requirements that are essential for the storage of XML documents. As a result of our study, we designed the Access Support Tree and TextArray (AST/TA) data structure. The important idea of the AST/TA data structure is the separation of the (logical) structure of a document from its "visible" text content. The latter is represented as a single contiguous string. At the same time the AST/TA data structure provides a tight integration to guarantee consistent changes. We introduce the AST/TA data structure formally by its abstraction, namely the AST/TA model and compare requirements of our AST/TA approach with those found in the current literature. Finally, we describe the advantage of the AST/TA model based on the AST/TA design principles.

The XML Query Execution Engine (XEE)

“…Based on this observation, we designed our AST/TA data structure [22]. We distinguish the Access Support Tree and , is incorporated and stored in an ordered tree-the Access Support Tree (AST).…”

“…In our example, all offsets are equal to 0, since we assume the document not being updated yet. For conceptual details of our AST/TA data structure, we refer to [22]. The AST/TA data structure is especially designed for update functionality, a feature that is often neglected in other approaches.…”

“…TAs are designed for retrieving and writing arbitrary sequences of characters or words from or to the "visible" text content of XML documents [22]. To facilitate text or information retrieval support appropriately, TAs must provide both sequential and random access to text segments of documents they manage.…”

“…To facilitate text or information retrieval support appropriately, TAs must provide both sequential and random access to text segments of documents they manage. As TAs are designed for nonnormalized text (sequences of characters) and normalized text (sequences of words)-see [22], we provide generic access to TAs by a suitable interface. Furthermore, TAs are not of fixed length.…”

“…In contrast to other similar systems, the design of XEE is based on an alternative approach for managing XML documents and data. That is, we build the XEE system on top of an appropriate XML data type-the Access Support Tree (AST) and TextArray (TA) data structure [22]. To our best knowledge, the storage concept our data structure is based on has not been investigated yet in detail.…”