Message Sets: Specifying data element separation methods to model a message

Specify the appropriate method of data element separation to identify data elements in a TDS message.

Elements of data in a TDS message are identified according to the data element separation method that you must specify for the Data Element Separation property for a complex type. Depending on the value that you have set for Data Element Separation, the properties Tag Data Separator and Delimiter (for a message set and a complex type) might also be required to identify each element.

The following describes the methods that you can specify for each complex type. The examples given are all based on a complex type that contains three elements of type STRING. The Tag Data Separator, where used, is the colon (:), and the Delimiter, where used, is the asterisk (*).

Tagged Delimited

Each data value is preceded by a tag that is specified as an element property. If the tag has an associated Length of Tag, indicating that the tag has a fixed length, each data value follows immediately after the tag. If the tag is not specified as fixed length, the tag is separated from the next element by a Tag Data Separator. Each data value is separated from the next by a Delimiter. There is no Delimiter after the last element in the complex type.

The following example shows tags of fixed length:

 tag1data1*tag2data2*tag3data3

The following example shows tags of variable length:

 tag1:data1*tag11:data2*tag111:data3

Tagged Fixed Length

This method is the similar to Tagged Delimited, but the data values are always fixed length. Therefore, no delimiter is required after each data value. The tags themselves can be fixed length or variable length, depending the setting of Tag Data Separator and Length of Tag.

The following example shows tags of fixed length:

tag1data1tag2data2tag3data3

The following example shows tags of variable length:

tag1:data1tag11:data2tag111:data3

Tagged Encoded Length

This method has a tag and a length field before the data. It indicates to the parser that following each tag in the bit stream there is data defining the length of data to be associated with that tag. You must set the Length of Encoded Length parameter. If the value in Length of Encoded Length includes extra characters, you must also set the Extra Chars in Encoded Length parameter.

The following example shows a tag of fixed length of four characters (Length of Tag has been set to four), a three-character length field (Length of Encoded Length has been set to three), and several characters of data. Extra Chars in Encoded Length has been set to zero:

tagA007dataAAAtagB006dataBBtagC009dataCCCCC

Given the bit stream above, the parser finds the tag "tagA" and extracts the length value 7. Because Extra Chars in Encoded Length is set to zero, the next seven (7 - 0) characters are the data. Then follow the characters for the next tag "tagB" and the length value of 6, and so on for tag "tagC". In each case in this example, the value in the length field is exactly the length of data.

The following example shows tags with a fixed length of four characters (Length of Tag has been set to four), a three-character length field (Length of Encoded Length has been set to three), and several characters of data. Extra Chars in Encoded Length has been set to three (because in this example the length field value includes the three-character length field as well as the data field):

tagA012dataAAAAAtagB010dataBBBtagC016dataCCCCCCCCC

Given the bit stream above, after "tagA" the parser extracts the length value 12. But because Extra Chars in Encoded Length is set to three, only the next nine (12 - 3) characters are the data. Then follow the characters for "tagB" and length value 10, and so on. In each case in this example, the value in the length field is three more than the actual length of data.

All Elements Delimited

The data values have no tag, but each data value is separated from the next by a delimiter.

The following example shows this:

data1*data2*data3

Variable Length Elements Delimited

If a data element is fixed length, the next data value follows immediately after it. If the data element is variable length, the next data value is separated from it by the delimiter. There are no tags.

The following example shows element 2 as fixed length, and elements 1 and 3 as variable length:

data1*data2data3

Use Data Pattern

The data associated with each element is determined by the parser matching the data with the regular expression in the Data Pattern property for that element. The TDS parser uses the regular expression in the Data Pattern to:

Determine the length of data to associate with each element.
Determine if, in the case of a repeating element, another occurrence of an element is present in the bit stream.
Determine the presence (if the pattern is matched) or absence (if the pattern is not matched) of an element in the bit stream.

There are no delimiters or tags, other than those coded as part of the regular expression patterns. See Message Sets: Regular expression syntax for an explanation of how pattern matching works.

The following example shows three elements, each having the regular expression Data Pattern shown:

First Data Pattern = [A-Z]{1,3}
Second Data Pattern = [0-9]+
Third Data Pattern = [a-z]*

Message data = 'DT31758934information for you'

First element data: 'DT'
Second element data: '31758934'
Third element data: 'information'

The first Data Pattern means "from one to three characters in the range A to Z", the second means "one or more characters in the range 0 to 9", and the third means "zero or more characters in the range a to z". Notice how each element's data was terminated by the first character that did not match the element's Data Pattern.

Fixed Length

All elements are fixed length, and each data value immediately follows the next with no delimiter. There are no tags.

The following example shows this:

data1data2data3

Fixed Length AL3

This method is the same as Fixed Length, but it also notifies the parser to implement a number of rules in relation to missing elements, length encoding, and versioning that are predefined in the ACORD AL3 standard.

Undefined

This value is set automatically when you set the Type Composition property of a complex type to Message, and you cannot set it to any other value. You are also unable to set values for the TDS Type properties Group Indicator, Group Terminator, Tag Data Separator, Length of Tag, and Delimiter.

If you set the Data Element Separation method to Undefined, you must not set the Type Composition property to Empty, Choice, Unordered Set, Ordered Set, Sequence, or Simple Unordered Set.

For more information about Type Composition set to Message, see Message Sets: Multipart messages.