General picture: how to use
the XML standard
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Prerequisites for using XML
The use of the XML standards requires certain software tools. In the
simplest case, these are an XML processor and validator.
The XML processor is usually included in the application used to view
the XML document. It verifies whether the XML file is well formed, which
means that it follows all the rules defined in the W3C recommendation
for XML syntax.
The validator checks whether the XML instance document conforms to
the XML schema. XML schemas contain definitions and structures which
can be used in XML instance documents. The instance documents contain
the actual data with their respective tags in the form of elements and
their attributes. Validating software compares the instance document
to its schema. This includes checking that the document contains only
legal tags, if the data conforms to the format specified in the schema,
whether the structure of its content is correct, etc. One schema can
define multiple data representations, contained in different XML instance
documents. However, the content of all those documents must remain within
the limits and restrictions specified in the schema.
Validating different instances of XML business documents with one
schema
Validation can be used in business scenarios, where each of the trading
partners involved in the data exchange holds a copy of a standard schema
and validates each instance document sent or received. Of course, there
have to be separate schemas for each type of business document, as they
all have different content and structure, e.g. Order, Despatch Advice,
Invoice, etc. Documents that are not valid (do not conform to the respective
schema) are rejected. At the sender's side, the validating software
should be installed at the document generation point. Thus, each business
message is validated and the possible errors can be corrected before
sending.
Validating XML documents at the sender's side
At the receiver's side the validation takes place in the receiving
point of the exchange software, before any data is transmitted to the
users' business application.
Validating XML documents at the receiver's side
Usually, the XML tools combine the functionalities of parsing (extracting
data and tags from the native XML document), editing, checking well-formednes
and validating in one software unit, but there are also a number of
self contained validators and editors. For more information refer to
the XML Tools.
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GS1 set of XML standards
GS1 produces several work products as part of it’s standards
for implementation. Two of those work products are schemas
and Business Message Standards
or BMS.
Message standards allow users to convert business documents into a
format that can be electronically exchanged. XML business documents
are referred to as “messages”, or “documents”,
and their format is defined in the GS1 XML data format message standards.
The exchange of these business documents is a component of the overall
e-Commerce.
GS1 Schema describes the structure of an XML document. The purpose
of an XML Schema is to define the legal building blocks of an XML document,
GS1 schema design allows developers to supply information embedded within
XML documentation.
GS1 XML Standards are an organized suite of XML Schema Modules. The
current release is an architecture upgrade from the previous version.
The changes have been incorporated to take full advantage of all the
features of XML Schema specifications.
Business Message Standards are the artefact of the GSMP that documents
the formally approved standards for a business message. Each Business
Message Standard brings together the appropriate classes, attributes,
and values needed to fulfil the message objective. Specific definitions
are provided to ensure clarity around class, attributes, and values.
Syntax constraints are identified. The standard also includes the high
level and detail level class diagrams depicting the scope of the message,
and the relationship of its elements to each other. These diagrams allow
parties to see data relationships and to determine where and how to
interface extensions to fulfil a business function. Each standard contains
a series of extracts from the Global Data Dictionary. Relevant attribute
items within a specific class name are presented, identified by type
and use.
The GS1 XML standards are published as a set of documents per business
message. Users need to download all of those documents to implement
a given message. Those documents include:
Implementers packet
The implementer’s packet is a ZIP file, comprised of all the
XML files necessary for validating a given XML message. It consists
of:
- TableofContents.txt – a text file listing all the files included
in the given packet
- Instance File folder, containing one (out of many possible) sample
XML file for the message
- HTML Sample folder, containing the HTML representation of the sample
XML file from the Instance File folder
- Schemas folder, with the following content:
- EAN.UCC folder – contains two subfolders:
- Common – includes schemas from the common
library, with the target namespace: xmlns:eanucc="urn:ean.ucc:2".
These are files that can be reused in many business documents,
in any context
- [Business Process Area name] – includes schemas from
the particular business area that are necessary to validate
the given business message. These schemas have the target
namespace:
xmlns:[context-specific
prefix]="urn:ean.ucc:[context value(s)]:2"
For more details see Context
and Versioning
- SBDH folder – contains the Standard
Business Document Header schemas
- Proxy schema
– for the particular business message
Business Message Standard
(BMS)
This is the document containing Business Solution Document (BSD) for
the given message and the full UML model of the message.
The Global Data Dictionary report lists all the message model components
(classes, role names, enumerated values and attributes), their definitions,
cardinality, data field length and the title of the XML schema, where
those components are defined.
The purpose of the Business Message Standards is to provide the necessary
information to implement a particular message as a part of the GS1 System.
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Mapping from UML to XML
The GS1 XML standards are developed based on UML Class Diagrams. A
Class Diagram is mapped into an XML Schema or Schemas. Afterwards, a
sample XML file is developed, complying to data structures defined in
the schema and data definitions from the Global Data Dictionary. The
Class Diagrams with the model description and the sample XML file are
then used to create the Business
Message Standard, published together with the set of schemas.
The general picture of GS1 XML standards development
The actual mapping of the specific components of UML to
XML is driven by the XML syntax constraints and the chosen schema design
model. However, some general rules are applied whenever it is possible
(exceptions from those rules are rare and caused by the syntax constraints).
The user does not have to understand all the details and complexities
of UML to XML mapping, but the basic familiarity of key principles can
be helpful in reading the GS1 standards.
The basic rules for mapping of UML components to XML can be illustrated
by the three examples below:
Example 1
Mapping of UML components as XML Complex Types and Elements
Example 2
Mapping of UML components as XML Simple Types and Attributes
Example 3
Mapping of UML components as XML Choice
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