XPath Expression Part I

Before leaning FOR XML PATH option and XQuery, today, we'll learn about XPath Expression. This post will go over some XPath terminologies. Next post we'll look at the XPath syntax and work through some examples. If you want to learn more about XPath, please read the W3C XPath documentation here. W3schools website also has a good tutorial here.

Xpath (XML Path Language)
    Is a standard for define path to element in XML fragments/documents.
    Like a query language for XML
    Expressed in hierarchical way (like path in UNIX file system)
    Used in XQuery, XSLT, Xpointer, XML Schema
    Level are delimited with / character
    By default every column are element
    Prefix the column alias with @ character to covert column to attribute-centric formatting.

XPath Nodes:
    Root
    Element
    Attribute
    Text
    Namespace
    Comment
    Processing Instruction

XPath Axis: defines how a node-set(contain one or more node) is related to the current node.

Below are XPath Axes:
    Ancestor
    Ancestor-or-self
    Attribute
    Child
    Descendant
    Descendant-or-self
    Following
    Following-sibling
    Namespace
    Parent
    Preceding
    Preceding-sibling
    Self

Below is a drawing that summarize the axes. The drawing is not mine. I get the drawing from this website.

Reference:
W3Schools Xpath Tutorial
W3C Xpath 1.0
W3C Xpath 2.0