Index Structures for Path Expressions

Abstract

In recent years there has been an increased interest in managing data that does not conform to traditional data models, like the relational or object oriented model. The reasons for this non-conformance are diverse. On the one hand, data may not conform to such models at the physical level: it may be stored in data exchange formats, fetched from the Web, or stored as structured files. One the other hand, it may not conform at the logical level: data may have missing attributes, some attributes may be of different types in different data items, there may be heterogeneous collections, or the schema may be too complex or changes too often. The term semistructured data has been used to refer to such data. The semistructured data model consists of an edge-labeled graph, in which nodes correspond to objects and edges to attributes or values. Figure 1 illustrates a semistructured database providing information about a city.