XQuery Developer's Guide
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The World Wide Web Consortium (W3C) defines a set of language features and functions for XQuery. The BEA AquaLogic Data Services Platform XQuery engine fully supports language features with one exception (modules) and also supports a robust subset of functions and adds a number of implementation-specific functions and language keywords.
This chapter describes the function and language implementation and extensions in the XQuery engine.
The chapter includes the following topics:
Data Services Platform (DSP) supports the W3C Working Draft "XQuery 1.0 and XPath 2.0 Functions and Operators" dated 23 July 2004 (http://www.w3.org/TR/2004/WD-xpath-functions-20040723/ ). In addition, DSP supports a number of functions that are enhancements to the XQuery specification, which you can recognize by their extended function prefix fn-bea:. For example, the full XQuery notation for an extended function is: fn-bea:function_name.
This section describes the BEA XQuery function extensions, and contains the following topics:
Table 2-1 provides an overview of the BEA XQuery function extensions.
Data Services Platform (DSP) uses the role-base security policies of the underlying WebLogic platform to control access to data resources. A security policy is a condition that must be met for a secured resource to be accessed. If the outcome of condition evaluation is false — given the policy, requested resource, and user context — access to the resource is blocked and associated data is not returned.
Once the security policies have been configured using the Data Services Platform Console, you can use the security function extensions described in this section to determine:
This section describes the following DSP access control function extensions to the BEA implementation of XQuery:
The fn-bea:is-access-allowed function checks whether a user associated with the current request context can access the specified resource, which is denoted by a resource name and a data service identifier.
The function has the following signature:
where $resource is the name of the resource, and $data_service is the resource identifier.
This function makes a call to the WebLogic security framework to check access for the specified resource. An example is shown below.
if (fn-bea:is-access-allowed("ssn", "ld:DataServices/CustomerProfile.ds"))
then fn:true()
The fn-bea:is-user-in-group function checks whether the current user is in the specified group. This function analyzes the WebLogic authenticated subject for appropriate group membership.
This function has the following signature:
where $group is the group to test against the current user.
Note: This operation is not automatically authenticated.
The fn-bea:is-user-in-role function checks whether the current user is in the specified global role.This function obtains a list of roles from the WebLogic security framework.
The function has the following signature:
where $role is the role to test against the current user.
Note: This operation is not automatically authenticated.
The fn-bea:userid() function returns the identifier of the user making the request for the protected resource.
The function has the following signature:
This section describes the following duration, date, and time function extensions to the BEA implementation of XQuery:
The fn-bea:date-from-dateTime function converts a dateTime to a date, and returns the date part of the dateTime value.
The function has the following signature:
where $dateTime is the date and time.
fn-bea:date-from-dateTime(fn:dateTime("2005-07-15T21:09:44")) returns a date value corresponding to July 15th, 2005 in the current time zone.fn-bea:date-from-dateTime(()) returns an empty sequence.The fn-bea:date-from-string-with-format function returns a new date value from a string source value according to the specified pattern.
The function has the following signature:
where $format is the pattern and $dateString is the date. For more information about specifying patterns, see Date and Time Patterns.
fn-bea:date-from-string-with-format("yyyy-MM-dd G", "2005-06-22 AD") returns the specified date in the current time zone.fn-bea:date-from-string-with-format("yyyy-MM-dd", "2002-July-22") generates an error because the date string does not match the specified format.fn-bea:date-from-string-with-format("yyyy-MMM-dd", "2005-JUL-22") returns the specified date in the current time zone.The fn-bea:date-to-string-with-format function returns a date string with the specified pattern.
The function has the following signature:
where $format is the pattern and $date is the date. For more information about specifying patterns, see Date and Time Patterns.
fn-bea:date-to-string-with-format("by-dd-mm", xf:date("2005-07-15")) returns the string "05-15-07".fn-bea:date-to-string-with-format("yyyy-mm-dd", xf:date("2005-07-15")) returns the string "2005-07-15".The fn-bea:dateTime-from-string-with-format function returns a new dateTime value from a string source value according to the specified pattern.
The function has the following signature:
where $format is the pattern and $dateTimeString is the date and time. For more information about specifying patterns, see Date and Time Patterns.
fn-bea:dateTime-from-string-with-format("yyyy-MM-dd G", "2005-06-22 AD") returns the specified date, 12:00:00AM in the current time zone.fn-bea:dateTime-from-string-with-format("yyyy-MM-dd 'at' hh:mm", "2005-06-22 at 11:04") returns the specified date, 11:04:00AM in the current time zone.fn-bea:dateTime-from-string-with-format("yyyy-MM-dd", "2005-July-22") generates an error because the date string does not match the specified format.fn-bea:dateTime-from-string-with-format("yyyy-MMM-dd", "2005-JUL-22") returns 12:00:00AM in the current time zone.The fn-bea:dateTime-to-string-with-format function returns a date and time string with the specified pattern.
The function has the following signature:
where $format is the pattern and $dateTime is the date and time. For more information about specifying patterns, see Date and Time Patterns.
fn-bea:dateTime-to-string-with-format("dd MMM yyyy hh:mm a G", xf:dateTime("2005-01-07T22:09:44")) returns the string "07 JAN 2005 10:09 PM AD".fn-bea:dateTime-to-string-with-format("MM-dd-yyyy", xf:dateTime("2005-01-07T22:09:44")) returns the string "01-07-2005".The fn-bea:time-from-dateTime function returns the time from a dateTime value.
The function has the following signature:
where $dateTime is the date and time.
fn-bea:time-from-dateTime(fn:dateTime("2005-07-15T21:09:44")) returns a time value corresponding to 9:09:44PM in the current time zone.fn-bea:time-from-dateTime(()) returns an empty sequence.The fn-bea:time-from-string-with-format function returns a new time value from a string source value according to the specified pattern.
The function has the following signature:
where $format is the pattern and $timeString is the time. For more information about specifying patterns, see Date and Time Patterns.
fn-bea:time-from-string-with-format("HH.mm.ss", "21.45.22") returns the time 9:45:22PM in the current time zone.fn-bea:time-from-string-with-format("hh:mm:ss a", "8:07:22 PM") returns the time 8:07:22PM in the current time zone.The fn-bea:time-to-string-with-format function returns a time string with the specified pattern.
The function has the following signature:
where $format is the pattern and $time is the time. For more information about specifying patterns, see Date and Time Patterns.
fn-bea:time-to-string-with-format("hh:mm a", xf:time("22:09:44")) returns the string "10:09 PM".fn-bea:time-to-string-with-format("HH:mm a", xf:time("22:09:44")) returns the string "22:09 PM".You can construct date and time patterns using standard Java class symbols. Table 2-2 outlines the pattern symbols you can use.
Repeat each symbol to match the maximum number of characters required to represent the actual value. For example, to represent 4 July 2002, the pattern is d MMMM yyyy. To represent 12:43 PM, the pattern is hh:mm a.
This section describes the following DSP execution control function extensions to the BEA implementation of XQuery:
The fn-bea:async function evaluates an XQuery expression asynchronously, using a buffer to control data flow between threads of execution.
The function has the following signature:
fn-bea:async($expression as item()*, $cap as xs:integer) as item()*
where $expression is the XQuery expression to evaluate asynchronously and $cap is the size of the buffer.
The fn-bea:async function enables asynchronous execution of Web services to reduce problems caused by the latency of these services. When used in this manner, a very small buffer size such as 1 or 2 is sufficient, as the time to produce the first token can be long while the production of subsequent tokens should be quicker.
In the following example, CUSTOMER is a database table while the getCreditScore functions are Web services offered by two credit rating agencies.
The fn-bea:fence function enables you to define optimization boundaries, dividing queries into islands within which optimizations should occur while preventing optimizations across boundaries. You might consider using the fn-bea:fence function when building a query incrementally.
The function has the following signature:
where $expression is the input expression.
The fn-bea:fence function is a pass-through function that does not change the input stream, but indicates to the optimizer that global rewritings should not occur across itself. Specifically, the fn-bea:fence function stops the following rewritings: view unfolding, loop unrolling, constant folding, and Boolean optimizations.
The fn-bea:if-then-else function examines the value of the first parameter. If the condition is true, DSP returns the value of the second parameter (then). If the condition is false, DSP returns the value of the third parameter (else). If the returned condition is not a Boolean value, DSP generates an error.
The function has the following signature:
where $condition is the condition to test, $ifValue is the value to return when the condition evaluates to true, and $elseValue is the value to return when the condition evaluates to false.
fn-bea:if-then-else (xf:true(), 3, "10") returns the value 3.fn-bea:if-then-else (xf:false(), 3, "10") returns the string value 10.fn-bea:if-then-else ("true", 3, "10") generates a compile-time error because the condition is a string value and not a Boolean value.The fn-bea:timeout function returns either the full result of the primary expression, or the full result of the alternate expression in cases when the primary XQuery expression times out.
The function has the following signature:
where $expression is the primary XQuery expression to evaluate, $millisec is the time out value in milliseconds, and $alt is an alternative XQuery expression to evaluate after a time out has occurred.
You can use the fn-bea:timeout function in the following ways:
Note that the fn-bea:timeout function immediately returns the alternative expression in cases when accessing the data source causes an error. Also, an instance of fn-bea:timeout that has failed over to the alternate expression once will not re-evaluate the original expression during the same query evaluation.
$param is a external parameter
This section describes the following numeric function extensions to the BEA implementation of XQuery:
The fn-bea:format-number function converts a double to a string using the specified format pattern.
The function has the following signature:
where $number represents the double number to be converted to a string, and $pattern represents the pattern string. The format of this pattern is specified by the JDK 1.4.2 DecimalFormat class. (For information on DecimalFormat and other JDK 1.4.2 Java classes see: http://java.sun.com/j2se/1.4.2.)
The fn-bea:decimal-round function returns a decimal value rounded to the specified precision (scale) or to the nearest whole number.
The function has the following signatures:
where $value is the decimal value to round and $scale is the precision with which to round the decimal input. A scale value of 1 rounds the input to tenths, a scale value of 2 rounds it to hundreths, and so on.
fn-bea:decimal-round(127.444, 2) returns 127.44.fn-bea:decimal-round(0.1234567, 6) returns 0.123457.The fn-bea:decimal-truncate function returns a decimal value truncated to the specified precision (scale) or to the nearest whole number.
The function has the following signatures:
where $value is the decimal value to truncate and $scale is the precision with which to truncate the decimal input. A scale value of 1 truncates the input to tenths, a scale value of 2 truncates it to hundreths, and so on.
This section describes the following function extensions to the BEA implementation of XQuery:
The fn-bea:get-property function enables you to write data services that can change behavior based on external influence. This is an implicit way to parameterize functions.
The function first checks whether the property has been defined using the DSP Console. If so, it returns this value as a string. In cases when the property is not defined, the function returns the default value.
The function has the following signature:
where $propertyName is the name of the property, and $defaultValue is the default value returned by the function.
The fn-bea:inlinedXML function parses textual XML and returns an instance of the XQuery 1.0 Data Model.
The function has the following signature:
where $text is the textual XML to parse.
fn-bea:inlinedXML("<text</e>") returns element "e".fn-bea:inlinedXML("<?xml version="1.0"><e>text</e>") returns a document with root element "e".The fn-bea:rename function renames an element or a sequence of elements.
The function has the following signature:
where $oldelements is the sequence of elements to rename, and $newname is an element from which the new name and type are extracted.
For each element in the original sequence, the fn-bea:rename function returns a new element with the following:
In the above, if CUSTOMER() returns:
<CUST><FIRST_NAME>John</FIRST_NAME><LAST_NAME>Jones</LAST_NAME></CUST>
<CUSTOMER><FNAME>John</FNAME><LNAME>Jones</LNAME></CUSTOMER>
This section describes the following QName function extensions to the BEA implementation of XQuery:
The fn-bea:QName-from-string function creates an xs:QName and uses the value of $param as its local name without a namespace.
The function has the following signature:
where $name is the local name.
This section describes the following sequence function extensions to the BEA implementation of XQuery:
The fn-bea:interleave function interleaves the specified arguments. The function has the following signature:
where $item1 and $item2 are the items to interleave.
For example, fn-bea:interleave((<a/>, <b/>, </c>), " ") returns the following sequence:
This section describes the following string function extensions to the BEA implementation of XQuery:
The fn-bea:match function returns a list of two integers specifying the characters in the string input that match the input regular expression (or an empty list, if none found). When the function returns a match, the first integer represents the index of (the position of) the first character of the matching substring and the second integer represents the number of matching characters starting at the first match. The function has the following signature:
where $source is the input string and $regularExp uses the standard regular expression language.
Table 2-3 presents regular expression syntax examples.
fn-bea:match("abcde", "bcd") evaluates to the sequence (2,3).fn-bea:match("abcde", ()) evaluates to the empty sequence ().fn-bea:match((), "bcd") evaluates to the empty sequence ().fn-bea:match("abc", 4) generates an error at compile time because the second parameter is not a string.fn-bea:match("abcccdee", "[bc]") evaluates to the sequence (2,1).The fn-bea:sql-like function tests whether a string contains the specified pattern. Typically, you can use this function as a condition for a query, similar to the SQL LIKE operator used in a predicate of SQL queries. The function returns TRUE if the pattern is matched in the source expression, otherwise the function returns FALSE.
The function has the following signatures:
where $source is the string to search, $pattern is the pattern specified using the syntax of the SQL LIKE clause, and $escape is the character to use to escape a wildcard character in the pattern.
You can use the following wildcard characters to specify the pattern:
You can include the % or _ characters in the pattern by specifying an escape character and preceding the % or _ characters in the pattern with this escape character. The function then reads the character literally, instead of interpreting it as a special pattern-matching character.
fn-bea:sql-like($RTL_CUSTOMER.ADDRESS_1/FIRST_NAME,"H%","\") returns TRUE for all FIRST_NAME elements in $RTL_CUSTOMER.ADDRESS that start with the character H.fn-bea:sql-like($RTL_CUSTOMER.ADDRESS_1/FIRST_NAME,"_a%","\") returns TRUE for all FIRST_NAME elements in $RTL_CUSTOMER.ADDRESS that start with any character and have a second character of the letter a.fn-bea:sql-like($RTL_CUSTOMER.ADDRESS_1/FIRST_NAME,"H\%%","\") returns TRUE for all FIRST_NAME elements in $RTL_CUSTOMER.ADDRESS that start with the characters H%.The fn-bea:trim function removes the leading and trailing white space.
The function has the following signature:
where $source is the string to trim. In cases when $source is an empty sequence, the function returns an empty sequence. DSP generates an error when the parameter is not a string.
fn-bea:trim("abc") returns the string value "abc".fn-bea:trim(" abc ") returns the string value "abc".fn-bea:trim(()) returns the empty sequence.fn-bea:trim(5) generates a compile-time error because the parameter is not a string.The fn-bea:trim-left function removes the leading white space.
The function has the following signature:
where $input is the string to trim.
fn-bea:trim-left(" abc ") removes leading spaces and returns the string "abc ".fn-bea:trim-left(()) outputs an error. The input is the empty sequence (similar to a SQL null) which is a sequence containing zero items.The fn-bea:trim-right function removes the trailing white space.
The function has the following signature:
where $input is the string to trim.
fn-bea:trim-right(" abc ") removes trailing spaces and returns the string " abc".fn-bea:trim-right(()) outputs an error. The input is the empty sequence (similar to a SQL null) which is a sequence containing zero items.The following functions from the XQuery 1.0 specification are not supported in current BEA XQuery engine implementation:
In addition to the support for XQuery functions and operators and the BEA extensions described previously, the W3C Working Draft "XQuery 1.0 and XPath 2.0 Functions and Operators" dated 23 July 2004 (http://www.w3.org/TR/2004/WD-xpath-functions-20040723/ ) allows implementors to use their discretion in implementing various aspects of the specification, as listed in Table 2-4.
This section describes the BEA XQuery language implementation, and contains the following topics:
The Data Services Platform (Version: 2.0.1) conforms to the W3C Working Draft "XQuery 1.0: An XML Query Language" dated 23 July 2004 (http://www.w3.org/TR/2004/WD-xquery-20040723/), with these exceptions:
Beyond compliance with the specification, BEA AquaLogic Data Services Platform's XQuery language implementation (the DSP XQuery engine) extends the XQuery language via the following:
BEA offers a group by clause extension to standard FLWOR expressions. The following EBNF shows the syntax of the general FLWGDOR:
flwgdorExpression := (forClause | letClause) (forClause
| letClause
| whereClause
| groupbyClause
| orderbyClause)* returnClause
groupbyClause := "group" [variable "as" variable] "by" (expression
["as" variable]) ("," (expression ["as" variable]))*
The remaining clauses referenced in the EBNF fragment follow the standard definition, as presented in the XQuery specification.
As an example, consider the case of grouping books by year, without loosing books that do not have a year attribute. Using standard XQuery, you would need to perform a self-join with the result of the fn:distinct-values function, concatenating the result of the self-join with the result for books without a year attribute.
The following illustrates the XQuery expression to accomplish this:
Using the BEA group by extension, you could write the same query as follows:
The FLWGOR expression conceptually builds a sequence of binding tuples, where the size of the tuple is the number of variables in scope at that point in the FLWGOR. In the example, the tuple at the group by clause consists of a single variable binding $book which binds to each book in the bib.xml document, one book at a time (Table 1).
The group by creates a new sequence of binding tuples with each output tuple containing variables defined in the group by clause. After the group by, all variables there were previously in-scope go out of scope.
In the example, the output tuple from the group by clause is of size two with the variable bindings being for $year and $partition (Table 2).
The number of output tuples is equal to the number of unique group by value bindings. In the above example, this is the number of unique book/@year values: 2. The variable introduced in the group clause ($partition in the example above) binds to the sequence of all matching input values.
This extension enables external consumers of XML generated by XQuery to have certain empty elements and attributes omitted. You can specify this using optional indicators, instead of employing computed constructors, conditional statements, and custom functions.
For example, consider the following query:
<a><b>{()}</b><c foo="{()}"/></a>,
The extension enables the following to be returned:
<a><c/></a>
<a><b/><c foo=""/></a>
The extension uses the optional indicator '?' with direct element and attribute constructors. This mean that in the following you could change the production DirElemConstructor to the following:
[94] DirElemConstructor ::= "<" QName "?"? DirAttributeList
("/>" | (">" DirElemContent* "</" QName S? ">")) /* ws: explicit */
Likewise, you could change the DirAttributeList to the following:
[95] DirAttributeList ::= (S (QName "?"? S? "=" S?
DirAttributeValue)?)*
When ? is present, elements with no children and attributes with the value "" are omitted. The query in the example could then be written as:
<a><b?>{()}</b><c foo?="{()}"/></a>
which produces the following result:
<a><c/></a>
In another example, consider the case of constructing a new customer element with different tags. One requirement is that you do not want a phone element in the resulting customer when the phone number does not exist in the original customer. Using standard XQuery, you would have to write:
Using the optional element constructor, you could instead write the following:
Similarly, when you want the resulting customer element to use attributes instead of elements, you would need to employ computed attribute constructors using standard XQuery, as illustrated by the following:
Using the optional attribute constructor, the query becomes:
In addition, for some aspects of language processing, the W3C working draft document leaves the details to the implementor's discretion, but requires each implementor to specify and document the implementation details. All such "implementation defined1" language features of the XQuery language as implemented in BEA AquaLogic Data Services Platform Version: 2.0.1 are listed in Table 2-7.
Table 2-7 Implementation-Defined Values
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