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<field_type> <field_name> : <field options> ;

Primitive Field Types

The following primitive types are supported:

external MSP_BILLING_EVENT 
 { 
 msp_length l : external_only; 
 ascii v : dynamic_size(l); 
 };

external MySubUDR { 
  int  dataLength : static_size(1); 
  ascii secretData : dynamic_size(dataLength); 
 }; 
 external MyUDR { 
  int elementCount  : terminated_by(":"); 
  list<MySubUDR> myList : element_count(elementCount); 
  int userType  : terminated_by(0xA); 
 };

element_count(<expr>) 

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Field Options for Optional Fields

The following field options are used to specify when a field is present.

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external SimpleSequential {
    int recordType : static_size(1);
    ascii secretData : dynamic_size(remaining_size);
};

Bit Blocks

Bit blocks are used when the data record contains fields that are not byte aligned. When declaring fields in bit blocks there are two ways to specify which bits to use for the field content. When using a bit_block of a single byte, it is possible to specify the most and least significant bit of the field using msb and lsb, as previously described. The alternative is to use the bit_size option to specify the number of bits spanned by the field.

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Except for simple fields, a bit_block can contain repeat_block constructs in the contents part. For a description of repeat_block see the section below, Repeat Blocks.

Repeat Blocks

A repeat_block can be used to specify that a group of fields is to be repeated a specified number of times. Currently this construct can only be used inside bit_block structures or another repeat_block structure. However this is restricted to a maximum of two levels of repeat_block. See the example below.

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external BitBlockTest {
   bit_block : dynamic_size(remaining_size){
    int string_count: bit_size(8); 
    repeat_block(string_count) {
       int string_length: bit_size(8);
       repeat_block(string_length) {
         int character: bit_size(8);
       };
     };
   };
};

external MyParentFormat {
  int field1 : static_size(4);
  MyEnclosedFormat field1;
};

set Construct

The set construct is used for decoding formats containing optional blocks of additional data. The syntax of the set Construct is declared as follows:

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If a size is not specified on the set level, Ultra cannot validate that all the data in the UDR has been decoded. The user is therefore recommended to specify the size, unless the set size in advance is unknown (for instance if the record is terminated by a terminator package or the set size calculation is needed for the record size calculation). The dynamic_size(remaining_size) specification used in the previous example is often correct.

switched_set Construct

The switched_set construct can often be used instead of the set construct. It has advantages (in performance and in ease of usage) especially when the separate sub-packages are simple. The syntax is however more complex compared to the basic set construct. The syntax of the switched_set construct is declared as follows:

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external SwitchedSetExample: terminated_by(0xA) { 
   // Size is remaining_size -1 (minus the terminator linefeed) 
    switched_set( packageId ): 
        dynamic_size( remaining_size - 1 ) { 
      ascii packageId: int(base10), static_size(1); 
      ascii packageLength: static_size(1), int(base10), 
         encode_value( case_size - 2 ); 
      case(1) { 
         list<ascii> list1: 
            dynamic_size( packageLength ); 
      }; 
      case(2): include_prefix { 
         ascii packageId_3: int(base10), static_size(1), 
               encode_value(3), external_only; 
         ascii packageLength_3: int(base10), static_size(1), 
               encode_value(case_size - 2), external_only; 
         ascii body_3: dynamic_size( packageLength_3 ); 
      }; 
      default: include_prefix { 
       list<ascii> defaultContent: 
             dynamic_size( packageLength + 2 ); 
      }; 
   }; 
 };

Encoding Specifications and Expressions

To support encoding to binary formats, it is often necessary to explicitly specify which value to be encoded in the external fields. Normally the value is taken from the corresponding internal field, however there are cases when this is not desirable. For instance, if there is no mapped internal field (because the external_only option has been used), or the value must be calculated from information about the encoding (for instance, udr_size). This is done through the encode_value option and there are several special constructs that may be used in the value expression (see the section above, Primitive Field Types).

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