XML Values

An XML value is a value composed of XML elements and attributes, where elements can contain other XML elements or text. XML values can be created directly or built by parsing string values. XML values cannot be stored in records, but can be converted to string representation and stored in that form.

Operations on XML Values

You can declare a variable of xml type and assign it to XML values:

xml xmlVar;

In addition to declaring a variable for use with XML values, you can also perform the following operations:

xmlagg – Aggregate a number of XML values into a single value. This can be used only in aggregate windows or with event caches (see below). Use xmlagg with caution; it can consume a large amount of memory very quickly as it produces a large verbose string proportionate to the size of the contents of each group.
Syntax: xmlagg(xml value)

Type: The argument must be an XML value. The function returns an XML value.

Example: xmlagg(xmlparse(stringCol))
xmlconcat – Concatenate a number of XML values into a single value.
Syntax: xmlconcat(xml value ..., xml value)

Type: The arguments must be XML values. The function returns an XML value.

Example: xmlconcat(xmlparse(stringCol), xmlparse('<t/>'))
xmlelement – Create a new XML data element, with attributes and XML expressions within it.
Syntax: xmlelement(name xmlattributes(string AS name ..., string AS name) , xml value,...,xml value)

Type: The names must adhere to these conventions:
- A name is either a sequence of alphabetic characters, digits, and underscore characters, or a sequence of any characters enclosed in double quotation marks.
- If a name is not enclosed in double quotation marks, it must begin with an alphabetic character or an underscore.
- A name cannot contain spaces unless it is enclosed in double quotation marks.
- A name cannot be a Reserved Word unless it is enclosed in double quotation marks. Reserved words are case insensitive, so for example, a name cannot be “AND” or “and” or “AnD”.
- Columns cannot be named “rowid”, "bigrowtime", or “rowtime”.
The function returns an XML value.

Example: xmlelement(top, xmlattributes('data' as attr1), xmlparse('<t/>'))
xmlparse – Convert a string to an XML value.
Syntax: xmlparse(string value)

Type: The argument must be a string value. The function returns an XML value.

Example: xmlparse('<tag/>')
xmlserialize – Convert an XML value to a string.
Syntax: xmlserialize(xml value)

Type: The argument must be an XML value. The function returns a string.

Example: xmlserialize(xmlparse('<t/>'))

Example

CREATE  INPUT  WINDOW Trades
    SCHEMA (TradeId INTEGER, Symbol STRING, TradeInfo STRING)
    PRIMARY KEY (TradeId) ;

CREATE FLEX myFlex
    IN Trades
    OUT OUTPUT WINDOW TradeReport
    SCHEMA (TradeId INTEGER, TradeDesc STRING
    PRIMARY KEY (TradeId)
    outfile "output/TradeReport.out"
BEGIN
    ON Trades {
        xml u := xmlparse('<Option OptionId="8">10000</Option>');
        xml v := xmlparse(Trades.TradeInfo);
        xml w := xmlelement(Comment, xmlattributes(Trades.Symbol as Symbol), u, v);
        v := xmlconcat(u, v, w);
        output [TradeId = Trades.TradeId; TradeDesc = xmlserialize(v)];
    };
END;

CREATE  OUTPUT  WINDOW XmlAggregation
    SCHEMA (Symbol STRING, TradeDesc STRING)
    PRIMARY KEY DEDUCED
    outfile "output/XmlAggregation.out"
AS
    SELECT    Trades.Symbol AS Symbol
            , xmlserialize( xmlelement (  value
                                        , xmlattributes(Trades.Symbol as Symbol)
                                        , xmlagg( xmlparse(Trades.TradeInfo)))) AS TradeDesc
    FROM Trades
    GROUP BY Trades.Symbol;

The output for the TradeReport will be:

<TradeReport ESP_OPS="i" TradeId="1" TradeDesc="<Option OptionId="8">10000</Option><Transaction Price="15.4" Volume="1000"/><Comment Symbol="EBAY"><Option OptionId="8">10000</Option><Transaction Price="15.4" Volume="1000"/></Comment>"/> 
<TradeReport ESP_OPS="i" TradeId="2" TradeDesc="<Option OptionId="8">10000</Option><Transaction Price="5.4" Volume="2000"/><Comment Symbol="MSFT"><Option OptionId="8">10000</Option><Transaction Price="5.4" Volume="2000"/></Comment>"/>
<TradeReport ESP_OPS="i" TradeId="3" TradeDesc="<Option OptionId="8">10000</Option><Transaction Price="5.8" Volume="4000"/><Comment Symbol="MSFT"><Option OptionId="8">10000</Option><Transaction Price="5.8" Volume="4000"/></Comment>"/>

The output for the XMLAggregation will be:

<XmlAggregation ESP_OPS="i" Symbol="EBAY" TradeDesc="<value Symbol="EBAY"><Transaction Price="15.4" Volume="1000"/></value>"/>
<XmlAggregation ESP_OPS="i" Symbol="MSFT" TradeDesc="<value Symbol="MSFT"><Transaction Price="5.4" Volume="2000"/></value>"/>
<XmlAggregation ESP_OPS="u" Symbol="MSFT" TradeDesc="<value Symbol="MSFT"><Transaction Price="5.8" Volume="4000"/><Transaction Price="5.4" Volume="2000"/></value>"/>