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ABENST_TT_GROUP - ST TT GROUP

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- tt:group, Grouping

tt:group>
  tt:$[s-$|d-$]cond $[frq="..."$] ...
  tt:$[s-$|d-$]cond $[frq="..."$] ...
  ...
/tt:group>

Effect

During deserializations, the statement tt:group can be used to react to variable XML input streams containing groups of related elements in free order. Hereby, a list of cases is specified in tt:group, where the syntax of each case is formulated by a conditional transformation, namely a subelement tt:$[s-$|d-$]cond. In this case, tt:$[s-$]cond defines a serialization-relevant case, and tt:$[d-$]cond a deserialization-relevant case. Other direct subelements are not possible in tt:group. The statement tt:group can be a subelement of tt:$[s-$|d-$]cond.

In contrast to conditional transformations outside of tt:group, specifying at least one attribute using, data or check for a case is not necessary, provided that the content of tt:$[s-$|d-$]cond is not a pattern.

In the list of cases, the following must be noted:

Any number of serialization-relevant cases can be specified in which no attribute using, data, or check is specified.

Only one deserialization-relevant case that does not contain a pattern can be specified. This case is called standard deserialization.

To control how often a deserialization-relevant case must or can be executed in deserializations, tt:$[d-$]cond within tt:group can contain the additional attribute frq (frequency) with one of three allowed values:

/tt:$[d-$]cond ... frq="1" >

Required case. The case must be executed exactly once while the group is processed.

/tt:$[d-$]cond ... frq="?" >

Optional case. The case is executed only once while the group is processed.

/tt:$[d-$]cond ... frq="*" >

Multiple case. The case can be executed any number of times while the group is processed.

For frq="?" and frq="*", the expected element must not necessarily exist in the inbound XML stream.

Implicit frequency: If the attribute frq is not specified explicitly,

frq="1" is used implicitly in tt:cond cases that do not contain data conditions (that is, they must be executed in serializations).

frq="?" is used implicitly in tt:cond cases that contain a data condition (that, is they may not be executed in serializations).

Serialization

In serializations, the element tt:group is executed once as follows: All serialization-relevant cases with a met prerequisite or no prerequisite using, data, or check are executed in the given order.

Deserialization

In deserializations, the element tt:group starts a sequence of evaluation steps for the group that require some cases to be selected and additionally search for a superset of these cases to be selected. The group evaluation terminates successfully, when all required cases are selected or the current node does not match an unselected case.

Frequency 1: Mandatory case. The case is required and searched for.

Frequency ?: Optional case. The case is not required but searched for.

Frequency *: Fallback case. The case is neither required nor searched for.

During each evaluation step, one of the deserialization-relevant cases whose maximum case frequency has not yet been reached is selected as follows:

The first case that contains a suitable pattern is executed (deserialization and assertions met).
If no such case exists, the system tries to execute the standard deserialization, if it exists. If the possible prerequisites using, data, or check of the standard deserialization are not met, the exception CX_ST_REF_ACCESS is raised.
If no standard deserialization exists, the exception CX_ST_GROUP_MISSING_CASE is raised.

Example

The following transformation DEMO_ST_GROUP shows how groupings work:

Assume that an inbound XML stream has the following form:

X0>
   X1>1/X1>
   X1>2/X1>
   X2>3/X2>
   X2>4/X2>
   X3>5/X3>
   X4>6/X4>
/X0>

The deserialization proceeds as follows:

In the first evaluation step, element X1 is used and the first element X1 deserialized, where ROOT1 is set to 1.
In the second evaluation step, element X1 is used again because of condition tt:cond frq="*" and the second element X1 deserialized, where ROOT1 is set to 2.
In the third loop pass, element X2 is used and the first element X2 deserialized, where ROOT2 is set to 3.
In the fourth evaluation step, element X2 cannot be used again because of condition tt:cond frq="?". Instead, the second element X2 is skipped in the standard deserialization with tt:skip. Specifying count is necessary because otherwise all subsequent elements would be skipped.
In the fifth evaluation step, element X3 is used and the first element X3 deserialized, where ROOT3 is set to 5.
All required cases of the group have been selected, so the loop ends. The element X4 is deserialized outside of tt:group and ROOT4 is set to 6.

Open program DEMO_ST_GROUP to execute the example.

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