0. INTRODUCTION
1. SCOPE
   1. Functional definition
   2. Field of application
   3. Principles
2. REFERENCES
3. TERMS AND DEFINITIONS
   1. Standard terms and definitions
   2. Message terms and definitions
4. MESSAGE DEFINITION
   1. Segment clarification
   2. Segment index (alphabetical sequence by tag)
   3. Message structure
      1. Segment table

This specification provides the definition of the EDI implementation guide definition message (IMPDEF) to be used in Electronic Data Interchange (EDI) between trading partners involved in administration, commerce and transport.

The EDI implementation guideline definition message (IMPDEF) permits the exchange of implementation details of an EDI message, including its usage and its presentation.

The EDI implementation guide definition message may be used for both national and international applications. It is based on universal practice related to administration, commerce and transport, and is not dependent on the type of business or industry.

The IMPDEF message provides an EDI mechanism for describing the contents of a specific Message Implementation Guideline (MIG) or Implementation Convention (IC) for an EDI message that is capable of being specified in the Directory Definition message (DIRDEF). One occurrence of the message shall contain only one MIG. An IMPDEF message for the message being implemented may contain:

a. the specification of the implementation usage b. additional implementation guidance c. presentation and processing guidance

The IMPDEF message shall describe usage of all necessary components (segment groups, segments, composite data elements, simple data elements and code values) from an identified source message, together with additional components (non-coded data values or ranges), to effect an implementation of the target message.

The IMPDEF message may describe those components which are not used. By default, those components of the source message which are not referenced, are not used in the implementation.

The IMPDEF message shall identify the source message upon which it is based. This identification may reference the source message contained either in a standard directory or in a separate DIRDEF message.

The IMPDEF message shall contain a complete MIG or IC and it shall not be used for update or maintenance purposes.

The hierarchical nature of both the source and target message structure must be preserved in the IMPDEF message. For example, this means that segment group information must be located immediately after the segment context of the trigger segment is established. Similarly, constituent element information must immediately follow the establishment of a segment or composite context, as must coded or non-coded values their element context.

The main body of the MIG is carried by repeated instances of the DFN loop. This loop can be used to encapsulate blocks of components and place them in any given prevailing context. It can also be used to define aliases or constraint blocks. In ordinary use, the DFN segment acts as a device to allow the logic flow to cycle through the optional segment groups inside the DFN-triggered segment group in the correct order to follow the hierarchical message structure. The segment groups within the DFN-triggered segment group are ordered so as to minimise the number of repeats within ordinary use.

The IMPDEF message maintains a context through the use of the segment groups within the DFN-triggered segment group. The DFN segment provides a means to redefine or re-establish the current context. The segment group that follows the DFN segment (and its associated FTX segment[s]) determines which context is being changed. For example, in normal message hierarchy sequence, codes are defined for elements within segments. To revert back to the segment context, a DFN segment would be followed by an ELU segment; similarly, to change the segment context, a DFN segment would be followed by an SGU segment. However, components such as repeats, references or relationships are considered to be applied in the context at which they are defined. Thus repeats, references, relationships or data representations may be applied to the whole message, individual segments, elements or composites.

When the DFN is used to perform encapsulation, the current context is considered to be stacked upon entry, inherited within, and restored upon exit. However, any encapsulated block may establish its own context at any time, either retaining or discarding any or all of the inherited context. Upon exit, the previous context is re-established, but may be immediately modified, in whole or part, by the components that follow the closing DFN segment.

The ordering of the components is governed by the source message hierarchy. Whilst the components at any particular level may be carried in any order, the message hierarchy must be maintained. This means that usage requirements of data elements within a segment must follow the usage requirements of that segment, but may themselves be presented in any order. Similarly, usage requirements of individual segments within a segment group must follow the trigger segment and the group definition and be presented together, but in any order.

Where constraints are used, and a constraint is active either because the constraint expression at the start of the constraint is true or because the implicit context of the constraint definition is active, then the usage specifications inside the constraint block shall prevail against those which would apply were the constraint not active. For example, if a segment is implicitly 'Not Used' by not being mentioned in the main body of the MIG or IC, but is explicitly tagged as 'Required' within an active constraint, then the prevailing usage shall be 'Required'. Conversely, if a segment is explicitly used in the main body of the MIG or IC, and also explicitly tagged as 'Not Used' within an active constraint then the prevailing usage shall be 'Not Used'.

The Interchange header shall specify character set level C.

See UNTDID, Part 4, Chapter 2.3 UN/ECE UNSM - General Introduction, Section 1.

See UNTDID, Part 4, Chapter 2.3 UN/ECE UNSM - General Introduction, Section 2.

The following additional definitions are for constituent parts of a message whose implementation is being described within an IMPDEF message:

Alias: this is used to describe a group of components collected together and named for frequent or repetitive use.

Component: this is used in a generic sense to apply to any item which may be a part of, or referenced by a part of a MIG. Thus it may refer to a segment, a segment group, a simple or composite element, a code list or individual code or non-coded value. It may also refer to structures such as an alias or a constraint within a MIG.

Constraint: this is used to describe a group of components with either an explicit or implicit constraint expression, which may be named for error reporting and context determination.

Source Message: this is used to refer to the original message specification as published in the relevant standard by the responsible authority.

Target Message: this is used to refer to the resultant message specification produced by applying the restrictions, clarifications and constraints contained within the MIG to the Source Message.

This section should be read in conjunction with the segment table which indicates mandatory, conditional and repeating requirements.

0010 UNH, Message header

A service segment starting and uniquely identifying a message. The message type code for the EDI implementation guide definition message is IMPDEF.

Note: EDI implementation guide definition messages conforming to this document must contain the following data in segment UNH, composite S009:

0020 BGM, Beginning of message

A segment to indicate the beginning of the message and to transmit function, type and number of the message.

0030 MSG, Message type identification

A segment identifying a message type to which the implementation details apply.

0040 RCS, Requirements and conditions

A segment specifying the distribution conditions for the implementation.

0050 DII, Directory identification

A segment specifying the identity of the source directory set and giving its language and maintenance operation. This identifies the underlying standard from which the standard message is drawn.

0060 RFF, Reference

A segment carrying reference information for the implementation as a whole. This may specify the unique registration identifier of this implementation guide; it may carry references to graphical information to be used or displayed whenever the implementation is physically displayed.

0070 DTM, Date/time/period

A segment specifying dates related to the implementation guide, such as date of issue or date of approval.

0080 FTX, Free text

A segment providing implementation guide notes which relate to the implementation as a whole. It may also carry various legal or contractual phrases which may apply to the ownership or copyright of the implementation guide, or contractual terms which will be incorporated by reference into any contract of which a data transmission using this implementation is a part.

0090 Segment Group 1: PNA-ADR-SG2

A group of segments identifying the parties involved in the transaction with associated information. For publicly available implementation guides this includes details of the ownership and origination of the guide.

0100 PNA, Party identification

A segment identifying the names of the parties involved in the transaction, e.g., originator, requester, author or secretariat.

0110 ADR, Address

A segment identifying the address of the party.

0120 Segment Group 2: CTA-COM

A group of segments identifying a person or a department and identifying communication type and number.

0130 CTA, Contact information

A segment identifying a person or a department for the party to whom the communication should be directed.

0140 COM, Communication contact

A segment identifying communication type and number of the person.

0150 Segment Group 3: DFN-FTX-SG4-SG5-SG6-SG7-SG8-SG9-SG10-SG11-

SG12 A group of segments to describe the usage of a segment, a segment group, a composite or an element, an alias, or a constraint in a MIG or IC. The iterations of this segment group form the bulk of the MIG or IC.

The MIG or IC consists of a series of iterations of this segment group which describe the target message hierarchy. Within the hierarchy, additional occurrences of this segment group may specify the conditions or relationships between the components.

Only the appropriate parts of this segment group should be used as necessary on any particular iteration. The other contained segment groups are ordered to minimise the number of iterations of this segment group. The 'Alias' and 'Constraint' instances of this segment group provide a mechanism for grouping or encapsulating blocks of components. An 'Alias' has no context, and therefore takes on the context of the point at which it is used. A 'Constraint' inherits the context in which it is defined, but may redefine any part of its context by using the appropriate optional segment groups within the main segment loop.

As well as its defining function, each component may also be used in a constraining manner. For example, a repeating segment may not only define its components, but also the number of times it is allowed to repeat; then, within each instance, a different combination of element requirements may be expressed. This conditionality may be based on either ordering or content criteria.

Once defined, an 'Alias' may be used throughout the MIG where required, by "using" the definition which is identified by its 'name'. Similarly, in error reporting, an active constraint may be identified by its 'name'.

0160 DFN, Definition function

A segment identifying the object of the definition, and containing an optional 'name' or identifier.

0170 FTX, Free text

A segment providing implementation guide notes pertaining to the preceding definition, or to carry the text of a constraint expression.

0180 Segment Group 4: GRU-FTX

A group of segments identifying a segment group and providing details about segment group usage. This segment group depends on a segment context having been established by an instance of a segment group describing segment usage.

This segment group defines a segment group context for the target message, and will immediately follow the definition of the trigger segment context, preceding the constituent elements within the trigger segment.

Several instances of the same segment group may be described, with the MEA segment group distinguishing which range or instance of the target message segment is being described.

0190 GRU, Segment group usage details

A segment specifying the usage of a segment group in a definition. The segment may identify one or more instances of a target segment group.

0200 FTX, Free text

A segment providing implementation guide notes or textual information related to the specific group in the underlying message.

0210 Segment Group 5: SGU-FTX

A group of segments specifying segment usage within the definition. There will be at least one instance of this segment group for each segment described in the implementation guide.

This segment group defines a segment context, and all the following components are deemed to be within the context of the segment whose usage is being defined until a subsequent segment context is defined.

Several instances of the same segment may be described, with the MEA segment group distinguishing which range or instance of the target message segment is being described.

0220 SGU, Segment usage details

A segment specifying the usage of a segment in a message type structure for this definition. As well as defining the specific usage of a particular target segment, this segment also provides the segment context for the following element usage details. The segment may identify one or more instances of usage for any particular segment in the target data message.

0230 FTX, Free text

A segment providing implementation guide notes, or textual information relating to the specific segment in the underlying message.

0240 Segment Group 6: FNT-REL-GIR-FTX

A group of segments specifying formalised relationships among the various components of this implementation at a particular context, such as additional rules concerning syntax and semantics which are specific to an implementation.

The relationships may be both intra-component, such as between elements in a segment, or inter-component, such as between elements in different segments.

Depending on the context in which this segment group is used, it may specify relationships between segments or segment groups in a message, between data elements in a segment, or between data elements in a composite.

0250 FNT, Footnote

A segment specifying a footnote identification number that may place the relationship in the current context.

0260 REL, Relationship

A segment specifying a relationship between the various components, typically data elements in a segment, in the current context.

0270 GIR, Related identification numbers

A segment identifying the various components in a relationship, typically data elements in a segment, in the current context.

0280 FTX, Free text

A segment carrying text notes to the preceding relationship.

0290 Segment Group 7: RFF-FTX

A group of segments carrying references, or constraints whose default context applies to the containing segment. This segment group may be used to change the constraint mechanism at the current and deeper levels in the message hierarchy. Additionally, this segment group may be used to carry legal and contractual terms which relate, either by way of explanation or to be incorporated by reference, in the particular context at which the group appears.

Depending on the context, the references may be applied to the target message as a whole, the current segment or element context, or the current code value context.

0300 RFF, Reference

A segment identifying a reference document or a following constraint expression.

0310 FTX, Free text

A segment carrying the text of a constraint expression or providing implementation guide notes pertaining to the preceding constraint.

0320 Segment Group 8: ELU-ELM-EDT-IMD-GIS-FTX

A group of segments specifying implementation requirements for data elements in the current segment or composite context. Multiple instances of this segment group will typically be used to describe the usage of all the elements in any given segment or composite context. There will be at least one instance of this segment group for each element used, although a constraint structure may override or further define the specification in any particular context or sub-context. The MEA segment group may be used to provide repeat range or specific instance information for repeating data elements.

This segment group defines an element or composite context which will remain in force until the next element or composite context is defined, or a new segment context is established.

0330 ELU, Data element usage details

A segment identifying the usage of a simple or composite data element in the current context. This segment starts a block of information about any one particular contextualised usage of a data element in a target data message.

The data element usage determines whether this segment is defining a composite context, a simple element context or a component element context.

0340 ELM, Simple data element details

A segment providing details of any variation or restriction of the current data element as used in this context. Typically this segment will convey details of restricted size or character representation.

0350 EDT, Editing details

A segment providing details of any editing information such as maximum field length and status that would be used by a screen-based editor, forms input or data output process when physical representation of the data carried in a data message using this implementation guide is required.

0360 IMD, Item description

A segment providing further details of presentational information such as text alignment and style that might be used by a screen-based editor, forms input or data output process when physical representation of the data carried in a data message using this implementation guide is required.

0370 X GIS, General indicator

A segment providing further details of processing information such as data handling, positioning or control that might be used by a screen-based editor, forms input or data output process when data is carried, stored or collected by a data message using this implementation guide is required.

0380 FTX, Free text

A segment providing implementation guide notes, or other textual information relating to this element usage. The segment will also be used to carry the final set of information that would be used by a screen-based editor; forms input or data output process; a legend or user-recognisable description; and a help text.

0390 Segment Group 9: MEA-FTX

A group of segments specifying implementation requirements for the number of instances of repeating segments, segment groups or elements in the current context. Multiple instances of this segment group will typically be used to describe both the overall limits of usage and to identify individual instances in any given context.

0400 MEA, Measurements

A segment to measure the number of instances of usage of a component in a message. The segment may specify minima, maxima, range or instance criteria.

0410 FTX, Free text

A segment providing implementation guide notes, or other textual information relating to this measurement.

0420 Segment Group 10: ELV-FTX

A group of segments specifying the usage of values for a non-coded data element. Multiple instances of this segment group may be used to provide a complete set of ranges or specific values, including preferences. It can be used for any other type of data element, such as strings, numerics, dates and times. It can also specify a default value and associated implementation notes for a specific element in a particular context.

A simple element or component element context must have been established before this segment group is used.

0430 ELV, Element value definition

A segment identifying one or more components of an element value constraint series. It also may provide a default value for the current element context. This is expressed in a single text field so as to be used by or applicable to the broadest range of applications.

0440 FTX, Free text

A segment providing implementation guide notes, or other textual information related to the particular context. Such a context may include implementation guide notes for the default value.

0450 Segment Group 11: CDV-FTX

A group of segments specifying the usage of code values for a coded data element. Multiple instances of this segment group may be used to provide a complete set of code values, including preferences.

A simple element or component element context must have been established before this segment group is used.

0460 CDV, Code value definition

A segment identifying the code value, its source and usage preference.

0470 FTX, Free text

A segment providing implementation guide notes, or other textual information related to the particular context.

0480 Segment Group 12: DRD-FTX

A group of segments specifying data representation details for a component of the message. This segment group may be used in a segment, group, composite or simple data element context to describe the data representation that the implementation guide author intends to use to hold, store or represent the structure or data in a non-EDI environment.

0490 DRD, Data representation details

A segment identifying an underlying data representation by tag, basic data type and size. This is the representation itself, and not a pointer to an external document.

0500 FTX, Free text

A segment providing implementation guide notes, or other relevant textual information.

0510 Segment Group 13: AUT-DTM

A group of segments to provide authentication for the message.

0520 AUT, Authentication result

A segment specifying the details of any authentication (validation) procedure applied to the IMPDEF message.

0530 DTM, Date/time/period

A segment specifying the date of authentication.

0540 UNT, Message trailer

A service segment ending a message, giving the total number of segments in the message (including the UNH & UNT) and the control reference number of the message.

	ADR	Address
	AUT	Authentication result
	BGM	Beginning of message
	CDV	Code value definition
	COM	Communication contact
	CTA	Contact information
	DFN	Definition function
	DII	Directory identification
	DRD	Data representation details
	DTM	Date/time/period
	EDT	Editing details
	ELM	Simple data element details
	ELU	Data element usage details
	ELV	Element value definition
	FNT	Footnote
	FTX	Free text
	GIR	Related identification numbers
	GIS	General indicator
	GRU	Segment group usage details
	IMD	Item description
	MEA	Measurements
	MSG	Message type identification
	PNA	Party identification
	RCS	Requirements and conditions
	REL	Relationship
	RFF	Reference
	SGU	Segment usage details
	UNH	Message header
	UNT	Message trailer

Change indicators
plus sign		An addition.
asterisk		Addition/substraction/change to a code entry for a particular data element.
hash or pound sign		Changes to names.
vertical bar		Changes to text for descriptions, notes and functions.
minus sign		A deletion.
letter X		Marked for deletion.