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574
Monadic Datalog and the Expressive Power of Languages for Web Information Extraction.
- Journal of the ACM
, 2004
"... Abstract. Research on information extraction from Web pages (wrapping) has seen much activity recently (particularly systems implementations), but little work has been done on formally studying the expressiveness of the formalisms proposed or on the theoretical foundations of wrapping. In this pape ..."
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Cited by 89 (10 self)
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Abstract. Research on information extraction from Web pages (wrapping) has seen much activity recently (particularly systems implementations), but little work has been done on formally studying the expressiveness of the formalisms proposed or on the theoretical foundations of wrapping. In this paper, we first study monadic datalog over trees as a wrapping language. We show that this simple language is equivalent to monadic second order logic (MSO) in its ability to specify wrappers. We believe that MSO has the right expressiveness required for Web information extraction and propose MSO as a yardstick for evaluating and comparing wrappers. Along the way, several other results on the complexity of query evaluation and query containment for monadic datalog over trees are established, and a simple normal form for this language is presented. Using the above results, we subsequently study the kernel fragment Elog − of the Elog wrapping language used in the Lixto system (a visual wrapper generator). Curiously, Elog − exactly captures MSO, yet is easier to use. Indeed, programs in this language can be entirely visually specified.
Context-Free Languages and Push-Down Automata
- HANDBOOK OF FORMAL LANGUAGES
, 1997
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On Verifying Consistency of XML Specifications
"... XML specifications often consist of a type definition (typically, a DTD) and a set of integrity constraints. It has been shown previously that such specifications can be inconsistent, and thus it is often desirable to check consistency at compile-time. It is known that for general keys and foreign k ..."
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Cited by 49 (8 self)
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XML specifications often consist of a type definition (typically, a DTD) and a set of integrity constraints. It has been shown previously that such specifications can be inconsistent, and thus it is often desirable to check consistency at compile-time. It is known that for general keys and foreign keys, and DTDs, the consistency problem is undecidable; however, it becomes NP-complete when all keys are one-attribute (unary), and tractable, if no foreign keys are used.
Efficient Incremental Validation of XML Documents
- In ICDE
, 2004
"... We discuss incremental validation of XML documents with respect to DTDs and XML Schema definitions. We consider insertions and deletions of subtrees, as opposed to leaf nodes only, and we also consider the validation of ID and IDREF attributes. For arbitrary schemas, we give a worstcase time an ..."
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Cited by 39 (2 self)
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We discuss incremental validation of XML documents with respect to DTDs and XML Schema definitions. We consider insertions and deletions of subtrees, as opposed to leaf nodes only, and we also consider the validation of ID and IDREF attributes. For arbitrary schemas, we give a worstcase time and linear space algorithm, and show that it often is far superior to revalidation from scratch. We present two classes of schemas, which capture most reallife DTDs, and show that they admit a logarithmic time incremental validation algorithm that, in many cases, requires only constant auxiliary space. We then discuss an implementation of these algorithms that is independent of, and can be customized for different storage mechanisms for XML. Finally, we present extensive experimental results showing that our approach is highly efficient and scalable.
