Electronic Data Interchange
The Data Element (UN/EDIFACT)

The Data Element is the smallest data structure in the standard.  It not only carries the actual data value, but also contains the properties that describe the data.  There are two types of data elements:

• Simple data element .  Simple data elements are stand alone data elements in a data segment.
• Component data element.  Sometimes referred to as sub elements, component data elements makes up the collection of data elements in a composite data  element structure.

Simple data elements and component data elements are fundamentally the same, but differ under the following:

• Different parent structure .  The simple data element belongs to the data segment, while the component data element belongs to the composite data structure.
• Repeating capability.  The simple data element can have multiple repeating instance under the data segment parent.  Meanwhile, a component data element cannot repeat under the composite element parent.

Outside of the difference above, in a nutshell, one can view all elements as simple data elements, and should they become part of a composite data structure do they become component data elements.  A data element can both be a simple data element and a component data element.

The data element has the following properties:

• Identifier.  A unique identifier that uniquely identifies the data element from other elements.
• Name.  The name of the data element.
• Minimum Length .  The minimum length of the value the data element can hold.
• Maximum Length .  The maximum length of the value the data element can hold.
• Data Type.  The data type of the value the data element can hold.
• Value.  The value of the data element.

In the context of a data segment or a composite element, the data element has the following additional properties:

• Position.  The position of the data element relative to other elements in the collection.  The data elements appear in the order of their sequential position.
• Requirement.  The required presence of the data element at the specified position as defined by the standard.
• User Requirement.  The custom requirement of a data element's presence at the specified position as implemented by a trading partner.  This requirement supersedes the standard Requirement, that is, if the standard requirement designates that the data element is optional (O,C) but the User Requirement indicates that it must be used (MUST USE) then the presence of the data element is required.  The data element is considered present if it has at least one character in its value. The following is a list of allowed user requirements:
  • MUST USE
  • USE
  • NOT USED
  • DEPENDENT
  • RECOMMENDED
  • NOT RECOMMENDED
• Maximum Repeat.  The number of times the data element can occur at the same position.  If the data element does not have repeating instances then this value is one.  This is applicable to simple data elements only; not applicable to component data elements.

Some data elements are constrained to having a list of values.  This list of code values is part of the data element definition, and it is in error if a data element should contain a value not part of this list.  The values in this list conform to the data requirement specified for the data element.  That is, they are within the minimum and maximum length of characters, and they are of the same data type.

Data Types

The following data types are available for the controlling agencies.

• Alphanumeric (an) – The data type represents data that is a combination of alphabetic or numeric characters.
  
• Alphabetic (a) – The data type represents data that is a combination of alphabetic characters.
  
• Numeric (n) - The data type represents a decimal number where the decimal number is stored in the data element with the decimal point explicitly included in the data.

Data Length

The length of data is the number of characters in the value.  One graphic character is counted as one character. Chinese and Japnaese characters may constitue two or three bytes for a single graphic character, which still counts as one character.  The following exceptions apply where some characters are not included in the count:

• The “+” sign that indicates that the number is positive should be suppressed from the data stream, but if it does occur, it is not included in the data length count.
  
• The “-“ sign that indicates that the number is negative is not included in the data length count.
  
• The decimal point is not included in the data length count.
  
• The trailing exponent indicator “E” is not included in the data length count. Example, 1E3.

Plus and Minus Signs

For decimal and numeric data types the minus/hyphen (“-“) sign preceding a number signifies a negative value while the plus (“+”) sign signifies a positive value. When no sign precedes the number, it is taken as a positive value. When transmitting any number that is positive, the “+” should always be suppressed.

Leading and Trailing Zeros

For decimal and numeric data types, leading zeros should be suppressed unless required to satisfy a minimum length requirement. For EDIFACT, when a decimal point precedes the first digit in the number, a single leading zero is required (example, 0.123). For X12, this leading zero is suppressed (example .123).

When only zeros follow a decimal point, the trailing zeros should be suppressed. However, if it becomes necessary to include the decimal point a single zero should follow the decimal point (example 123.0). Zeros after the decimal to indicate precision is also allowed.

For time data type in X12, the trailing zeros can also be used in decimal seconds to satisfy the minimum length requirement.

Triad Separators

For decimal and numeric data types, triad separators are not allowed. For example, the value "5,000,000,000" must be represented as "5000000000".

Spaces

For string, identifier, alphabetic and alphanumeric data types, trailing spaces are suppressed.  An element containing only spaces as its value is illegal.