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2.3. XML QUERY LANGUAGES 25 Parent-Axis: XPath: parent:: Short: .. The counterpart of the child-axis is the parent-axis that contains the parent node of the context-node, if there is one Ancestor-Axis: XPath: ancestor:: Short: NA The ancestor-axis contains the ancestors of the contextnode; the ancestors of the context-node consist of the parent of the context-node and the parent’s parent and so on; thus, the ancestor-axis will always include the root-node, unless the context-node is the root-node. Preceding-Axis: XPath: preceding:: Short: NA The preceding-axis contains all nodes that appear before the context-node in document order, excluding any ancestors and excluding any attribute nodes. Following-Axis: XPath: following:: Short: NA Similar to the preceding-axis the following-axis contains all nodes appearing after the context-node in document order, excluding any descendants and excluding attribute nodes. In addition to these axes there are some more that consist of the union of two axes like descendant-or-self or ancestor-or-self.
26 CHAPTER 2. FUNDAMENTALS Node Test Every axis has a principal node type: it is the type of nodes that the axis can contain. For the attribute-axis, the principal node type is attribute. For most other axes, the principal node type is element. A node test is true if and only if the type of the node is the principal node type and has a name equal to the specified name in the location step. For example, child::item selects the item children of the context-node. If the context-node has no item child element, it will select an empty set of nodes. A node test * is true for any node of the principal node type. For example, child::* will select all element children of the context-node, and attribute::* will select all attributes of the context-node. The node test text() is true for any text node. For example, child::text() will select all text nodes of the context-node. Similarly, the node test comment() is true for any comment-node. Predicates A predicate filters the node-set that is selected by the location step and drops all nodes that do not fulfill a condition. The general format of a predicate in a location step is [condition] where the square brackets are required, and condition represents some test resulting in a Boolean true or false value. For each node in the node-set to be filtered, an expression is evaluated with that node as the context-node. If the expression evaluates to true for that node, the node is kept in the node-set, otherwise it is dropped. The conditions in predicates are expressed by value comparisons and by nodeset functions. For instance, the predicate[name=’MP3 Player’] checks all name children if their content is equal to ’MP3 Player’. The context-node itself can be filtered with the self axis, e.g. [.=’MP3 Player’]. Value comparisons are used to check for equality (=) and inequality (≠, , ≥) of textual and numeric values. Conditions can be put together with the Boolean operators AND, OR and NOT . String functions like starts-with() are provided for textual comparisons. With node-set functions like last() or count properties of the node-set an be checked. A complete list of the string functions and node-set functions can be found in [126] respectively [132]. Predicates can be used recursively in the expressions of a predicate, e.g. /item[description[text = ’This item is ...’]].
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124 CHAPTER 7. THE XML INDEX UPDATE
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148 CHAPTER 8. KEYX IMPLEMENTATION
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170 BIBLIOGRAPHY [12] Alberto Capra
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172 BIBLIOGRAPHY [37] Roy Goldman a
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174 BIBLIOGRAPHY [59] Raghav Kaushi
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176 BIBLIOGRAPHY [84] David G. Mitc
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178 BIBLIOGRAPHY [113] W3 Schools.
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180 Index D, 78, 108, 110, 111, 144
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182 INDEX Oracle XML DB, 41 Parent,
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