Memory lower bounds for XPath evaluation over XML streams

Ramanan, Prakash

doi:10.1016/j.jcss.2010.10.004

Cited by 4 publications

(8 citation statements)

References 29 publications

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“…When Q has a mix of child and descendant axis steps, our algorithm uses O (d|Q | + nc) space and O ((|Q | + dn)|D|) time, in the worst case. For some worst case Q and D, this space requirement matches our lower bound in [28]; so, our algorithm uses optimal memory space in the worst case.…”

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confidence: 55%

“…The latter two algorithms use only O (c) space for storing information that might qualify the candidates for output. We [28] proved that any algorithm must use Ω(nc) space to store such information, for some worst case Q and D. So, the algorithms in [16,22] are incorrect. Our algorithm presented in this paper is from [26]; it is among the first correct algorithms known for the streaming version that also have a polynomial bound on the memory space and runtime.…”

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confidence: 99%

“…They also presented an Ω(r + log d) space lower bound, for each instance (Q , D). We present an algorithm (Section 5) that uses O (d|Q |) bits of space and O (|Q ||D|) time; as per our lower bound in [28], this algorithm uses optimal space for some worst case queries. Recently, Gou et al [16] presented a similar algorithm that uses O (r|Q | log d) bits of space and O (|Q ||D|) time.…”

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confidence: 99%

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Worst-case optimal algorithm for XPath evaluation over XML streams

Ramanan

2009

Journal of Computer and System Sciences

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We consider the XPath evaluation problem: Evaluate an XPath query Q on a streaming XML document D; i.e., determine the set Q (D) of document elements selected by Q . We mainly consider Conjunctive XPath queries that involve only the child and descendant axes. Previously known in-memory algorithms for this problem use O (|D|) space and O (|Q ||D|) time. Several previously known algorithms for the streaming version use Ω(d n ) space and Ω(d n |D|) time in the worst case; d denotes the depth of D, and n denotes the number of location steps in Q . Their exponential space requirement could well exceed the O (|D|)space used by the in-memory algorithms. We present an efficient algorithm that uses O (d|Q | + nc) space and O ((|Q | + dn)|D|) time in the worst case; c denotes the maximum number of elements of D that can be candidates for output, at any one instant. For some worst case Q and D, the memory space used by our algorithm matches our lower bound proved in a different paper; so, our algorithm uses optimal memory space in the worst case.

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Worst-case optimal algorithm for XPath evaluation over XML streams

Ramanan

2009

Journal of Computer and System Sciences

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“…Grohe, Koch, and Schweikardt show that Core XPATH, namely the full navigational fragment of XPATH 1.0 can be evaluated with height bounded memory [10]. Bar-Yossef, Fontoura, and Josifovski [2] study theoretical bounds as well as practical streaming algorithms for XPATH; more lower bounds for XPATH are given by Ramanan [21]. Shalem and Bar-Yossef [25] investigate twig-join algorithms over XML streams.…”

Section: Related Workmentioning

confidence: 99%

Transforming XML Streams with References

Maneth

Ordóñez

Seidl³

2015

String Processing and Information Retrieval

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Many useful XML transformations can be formulated through deterministic top-down tree transducers. As soon as transducers process parts of the input repeatedly or in an order deviating from the document order, such transductions cannot be realized over the XML document stream with constant or even depthbounded memory. Here we show that by enriching streams by forward references every such transformation can be compiled into a stream processor with a space consumption depending only on the transducer and the depth of the XML document. This is remarkable because tree transducers have rich restructuring capabilities and can process copies of input subdocuments independently. Also, references allow one to produce output in a compressed form which is guaranteed to be linear in the size of the input (up to the space required for labels). Our model is designed so that without decompression, the output may again serve as the input of a subsequent transducer. In order to reduce the extra overhead incurred by references, we investigate three optimizations: (i) reference reuse to save space, (ii) multi-labels to avoid chains of references and (iii) inlining to limit the use of references to deviations of the document order.

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“…It is shown that the maximal number of closed simultaneously alive answer candidates is a lower bound for "mostly all" nonrecursive trees in the sense of instance complexity. In [25], it is shown that for some queries in Fxp(ch, ch * , ∧) with independent ch predicates, the lower bound becomes n · c where n is the length of the selecting branch of the XPath expression, and c is maximal number of concurrently alive candidates. This shows that even compression tricks do not help for these query languages.…”

Section: Related Workmentioning

confidence: 99%

Streamable Fragments of Forward XPath

Gauwin

Niehren

2011

Implementation and Application of Automata

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Abstract. We present a query answering algorithm for a fragment of Forward XPath on Xml streams that we obtain by compilation to deterministic nested word automata. Our algorithm is earliest and in polynomial time. This proves the finite streamability of the fragment of Forward XPath with child steps, outermost-descendant steps, label tests, negation, and conjunction (aka filters), under the reasonable assumption that the number of conjunctions is bounded. We also prove that finite streamability fails without this assumption except if P=NP.

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Memory lower bounds for XPath evaluation over XML streams

Cited by 4 publications

References 29 publications

Worst-case optimal algorithm for XPath evaluation over XML streams

Worst-case optimal algorithm for XPath evaluation over XML streams

Transforming XML Streams with References

Streamable Fragments of Forward XPath

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