http://liacs.leidenuniv.nl/~stefanovtp/courses/StudentenSeminarium/Papers/FI2/AXML.pdf

Automata for XML---A survey

Linear delay enumeration and monadic second-order logic

The problem of selecting nodes in unranked trees is the most basic querying problem for XML. We propose stepwise tree automata for querying unranked trees. Stepwise tree automata can express the same monadic queries as monadic Datalog and monadic second-order logic. We prove this result by reduction to the ranked case, via a new systematic correspondence that relates unranked and ranked queries.

Querying unranked trees with stepwise tree automata

Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to relate complex properties of trees to the existence of tree automata for those properties. Furthermore, logics differ significantly in their model-checking properties, their automata models, and their behavior on ordered and unordered trees. In this paper we present a survey of logics for unranked trees.

/pdf/logics-for-unranked-trees-an-overview-3g6tex36n8.pdf

Logics for Unranked Trees: An Overview

We develop new algorithms for learning monadic node selection queries in unranked trees from annotated examples, and apply them to visually interactive Web information extraction.

We propose to represent monadic queries by bottom-up deterministic Node Selecting Tree Transducers (NSTTs), a particular class of tree automata that we introduce. We prove that deterministic NSTTs capture the class of queries definable in monadic second order logic (MSO) in trees, which Gottlob and Koch (2002) argue to have the right expressiveness for Web information extraction, and prove that monadic queries defined by NSTTs can be answered efficiently. We present a new polynomial time algorithm in RPNI-style that learns monadic queries defined by deterministic NSTTs from completely annotated examples, where all selected nodes are distinguished.

In practice, users prefer to provide partial annotations. We propose to account for partial annotations by intelligent tree pruning heuristics. We introduce pruning NSTTs--a formalism that shares many advantages of NSTTs. This leads us to an interactive learning algorithm for monadic queries defined by pruning NSTTs, which satisfies a new formal active learning model in the style of Angluin (1987).

We have implemented our interactive learning algorithm integrated it into a visually interactive Web information extraction system--called SQUIRREL--by plugging it into the Mozilla Web browser. Experiments on realistic Web documents confirm excellent quality with very few user interactions during wrapper induction.

/pdf/interactive-learning-of-node-selecting-tree-transducer-4uf2dimyv1.pdf

Interactive learning of node selecting tree transducer

Information extraction from semi-structured documents requires to find
n-ary queries in trees that define appropriate sets of n-tuples of
nodes. We propose new representation formalisms for 
n-ary queries by tree automata that we prove to capture MSO. We then 
investigate n-ary queries by unambiguous tree automata which are
relevant for query induction in multi-slot information extraction.
We show that this representation formalism captures the 
class of n-ary queries that are finite unions of Cartesian closed 
queries, a property we prove decidable.

N-ary Queries by Tree Automata.

We investigate n-ary node selection queries in trees by successful runs of tree automata. We show that run-based n-ary queries capture MSO, contribute algorithms for enumerating answers of n-ary queries, and study the complexity of the problem. We investigate the subclass of run-based n-ary queries by unambiguous tree automata.

/pdf/n-ary-queries-by-tree-automata-1lp48m9ean.pdf

Laurent Planque

Papers

N-ary Queries by Tree Automata.

N-ary queries by tree automata