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IADIS International Conference WWW/Internet 2010Table 1. Simbology for extended links.SimbolRepresentationElement of extended linkRemote resourcesub‐element arcsub‐element locatorreference through URIreference through labelSchemLinkbased‐ba_BankingActivities1href2fromd‐ba_TotalBankingActivitieshref3to4 from 6href5tod‐ba_TotalBankingActivitiesSubjectBIASchemaLinkbased‐ba_BankingActivitiesDomain1fromd‐ba_TotalBankingActivities4 to from 6tod‐ba_TotalBankingActivitiesSubjectBIAFigure 3. Low level representation of an extended link.Figure 4. High level representation of an extended link.3.3 Syntax and semanticThis section presents the XLPath sintactic mechanisms, accompanied of examples that demonstrate theirinterpretation. The basic structure of an XLPath query expression is similar to the location path of XPath,including the axis elements, element specification – analogue to the node specification of XPath – andpredicate. Besides those, to enjoy the advantages of the two navigation approaches suggested in Sections 3.2,the XLPath query expressions make use of a mechanism that indicates the level of abstraction. Thus,expressions preceded by LL navigate through the extended links structures according to the low levelapproach, while expressions preceded by HL navigate in high level.Axis Specification: The basic blocks of an expression location path of XPath are the location steps, whichdetermine the paths that conduct to the desired information in an XML document. These paths are directed bythe axis, which, in XPath, correspond mainly to the traditional relationships between nodes of XMLdocuments trees. In XLPath, the same principle is used, however with the difference of the paths, in this case,are determined by the references among the elements that compose the links networks. Graphically, thesereferences correspond to the lines and arrows that connect the elements as given in Figure 3 and in Figure 4.It is possible to realize that elements of the type arc are always associated to two link references: onethrough the attribute xlink:from and another through the attribute xlink:to, each one of them represented byan arrow, which identifies the directional character of this type of association. An important detail is that,from XLPath perspective, each one of these arrows is considered an arc. It means that there is a distinctionbetween arcs and elements of the arc type. This distinction is made to allow that XLPath access elements ofthe arc type like nodes of the links networks, navigating until them through arcs, i.e. references originatingfrom elements of the arc type. Thus, XLPath axes are used to specify the type of existing association betweenthe context element – equivalent to the context node of XPath – and the elements connected to it. These axesare: linked axis – directs the query to all the elements that refer or are referred by context element,including references by label and by URI; arc-source axis – directs the query to all the elements that are target nodes of arcs whose contextelement is the source;93