XML Query Routing in P2P Systems | Paper Critique

Critique on

XML Concern Acquisition in Structured P2P Systems

(Leonidas Fegaras, Weimin He, Gowtham Das, David Levine)

  • Rahul Rayineni

The structured peer-to-peer arrangement is a decentralized architectonics which consists of ample cardinal of nodes that allotment abstracts and assets with alternative nodes. They use a broadcast assortment table to actuate the area of data. The nodes in structured P2P systems maintains a account of neighbors so that they from a bury arrangement in which lookup time for a key booty logarithmic cardinal of acquisition hops amid peers. They action bigger availability and scalability than baggy P2P systems but the capital adversity in application these systems lies in abstracts adjustment and concern processing as queries are added complex. If the queries are not appropriately optimized acquisition and processing takes lot of time. This cardboard demonstrates about abstracts placement, querying, and indexing ample abstracts repositories broadcast over an absolute DHT based P2P systems like pastry (Reference 4 and 6).

According to Leonidas Fegaras, Weimen He, Gautam das, and David Levine, “There are lot of beforehand proposals like XPath lookup queries in P2P networks(Reference1) and Analysis abstracts sources in ample Broadcast Systems(reference 3) on indexing and querying XML abstracts broadcast abstracts over a P2P arrangement but there is no assignment appear on circuitous XML concern processing with abounding argument chase that uses abstracts synopses to selectively avenue queries to peers”.

The framework proposed in this cardboard is implemented on DHT-based P2P arrangement Pastry (Reference 4 and 6). But this framework can be implemented on any P2P infrastructure. This frameworks works on abbreviated abstracts namely structural abridgment and abstracts abridgment for mapping XML queries. The aerial concern acquisition precision, low abstracts adjustment and low aliment overheads are accomplished through atypical abstracts synopses structures. This framework gives added authentic appraisal of textual and ascendancy constraints in a concern compared to blossom filters.

The publishing action makes the abstracts accessible to alternative aeon while unpublishing is removing the certificate by the owner. If the associate wants to amend the certificate aboriginal it will unpublish the certificate and after broadcast it afresh to reflect the certificate updates. According to Leonidas Fegaras, Weimen He, Gautam Das, and David Levine,” The XPath syntax is adapted to add the assert e ~ S, area e is an approximate XPath announcement that allotment accurate if at atomic from the arrangement alternate by e matches the chase specification, S. A chase blueprint is an IR-style Boolean keyword concern that takes the form

“term” | S1 and S2 | S1 or S2 | (S)

where S, S1 and S2 are chase specifications. A appellation is a keyword that charge be present in the argument of an aspect alternate by the announcement e”.

The characterization aisle of an XML certificate consists of child/attribute accomplish and can analyze non-empty set of abstracts nodes in the document. There are two types of abstracts synopses acclimated in this framework in which one is agreeable synopses that accommodate structural arbitrary nodes associated with bit matrices. The added one is positional filters which are bit vectors consists of centralized anatomy arbitrary nodes and their positions. To accomplish acceptable amount antithesis with baby cardinal of nodes structural arbitrary advice and abstracts abridgment are broadcast over the absolute P2P network. This framework is able of award all accessible structural summaries applicative to the concern with one DHT lookup.

The agreeable synopses consists of basis agreement forth with their positions. Basis agreement are formed breaking the certificate in to simple terms. The position of the basis appellation depends on the position of its begin/end tags. The position of the elements tag depends on the cardinal of

the activate and end tags above-mentioned the elements. So basis agreement of a aforementioned aspect consists of aforementioned positional range. The positional bit agent consists of all the positions of the document.

According to Leonidas Fegaras, Weimen He, Gautam Das, and David Levine,” The chase blueprint e ~ t1 and t2 for two agreement t1 and t2 becomes accurate if and abandoned if there is at atomic one certificate bulge alternate by e that contains both terms. Application apparent appellation bitmaps alone, such as blossom filters, and blockage whether both the t1 and t2 $.25 are on, will accord us a prohibitive cardinal of apocryphal positives.”

The amount operation in this framework is containments filtering, CF(F,V) which analysis aspect containment. Here F is positional clarify and V is a bit vector. The achievement of the aloft action is new positional clarify F’. In the bit agent V, if there is at atomic one bit is on with in this ambit it copies all the $.25 in F to F’.

Data adjustment involves agreement of structural arbitrary and abstracts synopsis. The structural summaries are baffled to every associate application every altered tag name. Thus, with a distinct DHT lookup we can able to acquisition out all structural summaries analogous the structural brand of the query. The characterization aisle of abstracts abridgment is acclimated in agreement it. Back Multiple abstracts consists of characterization aisle , the abridgment from these abstracts is placed at a distinct peer. Thus with distinct DHT attending up we can locate all the documents. Concern acquisition involves accession and clarification abstracts all the way. The triples(peer, document, positional-filter) are acclimated as advice amid the peers. They accommodate id of a analogous certificate and buyer of the certificate forth with the certificate positions. At anniversary associate admeasurement of the account is bargain by removing the abstracts whose positional clarify are zeroes.

The arrangement updates like bulge arrival, abandonment and abortion are handled by atypical methods back the bulge arrives the bury network, it invokes the Pastry adjustment notifyReady() and alpha sending and accepting messages. It receives all the advice like structural summaries and abstracts synopses from its predecessor. Similarly back a bulge decides to leave the network, it routes all its structural summaries and abstracts synopses to its almsman and leave the network. This can be done application one distinct message. Back associate doesn’t acquisition a analogous structural arbitrary the antecedent bulge may be failed. In this case associate chooses addition tagname and chase appeal to alternative aeon to acquisition structural summary. The Id of the bootless antecedent is acclimated to analysis for the bulge failure. If the antecedent is bootless it will arrest the concern and browse the account afresh for the abstracts and accelerate a bulletin to administrator to broadcast the data. The capital advantage of this adjustment it will arrest abandoned one concern at a time and abstracts abridgment is adequate that is associated with the bootless peer

The abutting assignment to this is done by L.Galanis, Y.Wang, S. R.Jeffery, and D.J.DeWitt. analysis abstracts sources in ample broadcast systems.(Reference 3). In this framework, the broadcast indexing targets area of abstracts sources which is altered from the framework in this paper. The structural summaries are agnate to the one that are presented in this paper. Here they use the tag name of the aspect that accommodate the argument as chase key which is adverse to the framework in this cardboard in which argument was burst afore indexing and characterization paths are acclimated as keys. They don’t abode the indexing amount also. According to Leonidas Fegaras, Weimen He, Gautam Das, and David Levine, ” the framework proposed by Galanis (Reference 3) is added acceptable for data-centric XML abstracts rather than to document-centric ones, back the after may accommodate ample argument portions central specific tag names, which after-effects to the acquisition of ample genitalia of certificate to the aforementioned nodes.” Addition accompanying framework is by A. Bonifati, Xpath Lookup Queries in P2P Networks. WIDM 2004. in which XML abstracts bits are indexed based on their path. The chase key is the assortment amount of its path. This framework acknowledgment simple Xpath queries in one associate hop. The check of this framework is it requires added hops to retrieve circuitous abstracts fragment. Additionally this framework doesn’t abutment XPath predicates. There are alternative broadcast summaries for XML abstracts like XSketch(Reference 5) which is acclimated in selectivity admiration than in concern routing. In the cardboard presented by J.M. Bremer and M. Gertz on distributing XML repositories (Reference 2), the structural arbitrary is acclimated as a all-around arrangement to appearance how XML abstracts are burst and broadcast over the network.

My assessment of this paper, it provides best framework for XML acquisition in structured P2P networks. The abstracts abridgment and agreeable abridgment acclimated for indexing are bigger than approved blossom filters. The framework maps a concern with full-text chase into a broadcast affairs that migrates from associate to peer. The basis agreement acclimated in this framework are characterization paths which are bigger distinct tag names acclimated in the antecedent frameworks for acquisition XML data. The ascendancy clarification of this framework is able in acclamation the ascendancy relationships amid predicates in a query. It can acquisition all structural summaries of a concern application one DHT lookup. It can handle complicated XPath queries application structural summaries. The arrangement updates are handled finer application atypical methods which are actual acute in structured P2P networks. The abstracts adjustment action gives amount acclimation in the system. The framework is calmly scalable and it can be implemented on top of any absolute P2P infrastructure.


  1. A. Bonifati, et al. XPath Lookup Queries in P2P Networks. WIDM 2004.
  2. J.-M. Bremer and M. Gertz. On Distributing XML Repositories. WebDB 2003.
  3. L.Galanis, Y.Wang, S.R.Jeery, and D. J. DeWitt. Analysis Abstracts Sources in Ample Broadcast Systems. VLDB 2003.
  4. Pastry. http://freepastry .rice.edu/.
  5. N. Polyzotis and M. Garofalakis. Anatomy and Amount Synopses for XML Abstracts Graphs. VLDB 2002.
  6. A. Rowstron and P . Druschel. Pastry: Scalable, Broadcast Object Area and Acquisition for Large-Scale Peer-to-Peer Systems. International Conference on Broadcast Systems Platforms 2001.

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