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XSEarch, a semantic search engine for XML, is presented. XSEarch has a simple query language, suitable for a naive user. It returns semantically related document fragments that satisfy the user’s query. Query answers are ranked using extended information-retrieval techniques and are generated in an order similar to the ranking. Advanced indexing techniques(More)
Constraints are important not just for maintaining data integrity, but also because they capture natural probabilistic dependencies among data items. A <i>probabilistic XML database</i> (PXDB) is the probability sub-space comprising the instances of a <i>p-document</i> that satisfy a set of constraints. In contrast to existing models that can express(More)
Equivalence of aggregate queries is investigated for the class of conjunctive queries with comparisons and the aggregate operators count, count-distinct, min, max, and sum. Essentially, this class contains unnested SQL queries with the above aggregate operators, with a where clause consisting of a conjunction of comparisons, and without a having clause. The(More)
A framework for describing semantic relationships among nodes in XML documents is presented. In contrast to earlier work, the XML documents may have ID references (i.e., they correspond to graphs and not just trees). A specific <i>interconnection semantics</i> in this framework can be defined explicitly or derived automatically. The main advantage of(More)
The query equivalence problem has been studied extensively for set-semantics and, more recently, for bag-set semantics. However, SQL queries often combine set and bag-set semantics. For example, an SQL query that returns a multiset of elements may call a subquery or view that returns a set of elements. As another example, in SQL one can compute a(More)
SQL4X, a powerful language for simultaneously querying both relational and XML databases is presented. Using SQL4X, one can create both relations and XML documents as query results. Thus, SQL4X can be thought of as an integration language. In order to allow easy integration of XML documents with varied structures, SQL4X uses flexible semantics when querying(More)
The query equivalence problem has been studied extensively for set-semantics and, more recently, for bag and bag-set semantics. However, SQL queries often combine set, bag and bag-set semantics. For example, an SQL query that returns a multiset of elements may call a subquery or view that returns a set of elements. Queries may access both relations that do(More)