BeginningXmlDatabases

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Book review of Beginning XML Databases

Another book I find valuable ( for XML Databases in general ).
XPath 2.0 functions are conveniently divided into various categories:

• Accessor functions: These provide access to privately held data, privately held by other objects in other words, a function allowing access to setting and retrieving values of a property, without allowing direct access to the object containing the property. A read-only property has only one accessor function, and that allows retrieval of the property value. This is because a read-only property cannot be set.
• Errors and tracing: Raise errors and debug using tracing during processing.
• Constructor functions: These create an object instance from a class, or in really simplistic terms, they define a type. In other words, when declaring a variable as being of a simple data type such as a string or a number, in any programming language, one is constructing a variable. The mere definition of the variable as being of a specific type is actually a simple form of a constructor function. A constructor function constructs an iteration or copy of a variable from a definition.
• Numeric functions: As in any programming language, a numeric function performs some kind of conversion or calculation such that a number value is returned.
• String functions: As for number functions, but in this case a string is returned. Operations are usually performed on strings and return strings, rather than numbers, but not always.
• URI function: A URI function operates on a URI. What is a URI? A URI is a Uniform Resource Identifier. A URI is also a type of a URL (Universal Resource Locator).
• Boolean function: These functions produce a Boolean result, which programmatically allows for specific types of coding that result in either true or false.
• Functions on durations, dates, and times: These functions operate on return dates, times, and durations of time.
• QName functions: A QName is a qualified name. A QName contains a namespace URI. A QName is an optional prefix and a colon followed by a local name, or a URI plus a local element or attribute name.
• Node functions: These functions are applied specifically to XML document nodes.
• Sequence functions: A sequence is effectively a list of zero or more potentially repetitive items contained within a parent node. A sequence is therefore a collection. Sequence functions can be applied to a single collection as a whole, applying the same execution of a function to all elements in a collection at once.
• Context functions: These functions apply to the meanings and thus the metadata within an XML document.
• Other types of functions: These will not be demonstrated in this book as they are too obscure but are included at this stage so that you are aware of their existence:
  • Operators on base64Binary and hexBinary: Used for comparison of values where values do not have a decimal base (they are not decimal numbers).
  • Functions and operators on NOTATION: XML notation is a form of XML that is dialect-specific, and established for very specific applications in XML, such as [MathXML] and CML (chemistry). Specific XML dialect notations establish standards to, and apply topic regional semantics to otherwise generic XML data.

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