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The evaluation of path expression queries on semistructured data in a distributed asynchronous environment is considered. The focus is on the use of local information expressed in the form of path constraints in the optimization of path expression queries. III particular, decidabiity and complexity results on the implication problem for path constraints are(More)
We study the inference of Data Type Definitions (DTDs) for views of XML data, using an abstraction that focuses on document content structure. The views are defined by a query language that produces a list of documents selected from one or more input sources. The selection conditions involve vertical and horizontal navigation, thus querying explicitly the(More)
We study the typechecking problem for XML transformers: given an XML transformation program and a DTD for the input XML documents, check whether every result of the program conforms to a specified output DTD. We model XML transformers using a novel device called a <italic>k</italic>-pebble transducer, that can express most queries without data-value joins(More)
Motivated by formal models recently proposed in the context of XML, we study automata and logics on strings over infinite alphabets. These are conservative extensions of classical automata and logics defining the regular languages on finite alphabets. Specifically, we consider register and pebble automata, and extensions of first-order logic and monadic(More)
There is a fundamental mismatch between the hardness of database queries and their Turing complexity. For example, the even query on a set has low Turing complexity but is by all accounts a hard query. The mismatch is due to the abstract, genen’c nature of database computation: data items which are indistinguishable by logical properties are treated(More)
We formalize and study business process systems that are centered around "business artifacts", or simply "artifacts". Artifacts are used to represent (real or conceptual) key business entities, including both their data schema and lifecycles. The lifecycle of an artifact type specifies the possible sequencings of services that can be applied to an artifact(More)