OMG XMI 2.5.1：最新版UML数据模型交换标准

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OMG (Object Management Group) 的 XML Metadata Interchange (XMI) Specification Version 2.5.1 是一个重要的技术标准，它于2015年6月更新，文档编号为formal/2015-06-07。XMI是MDA (Model Driven Architecture) 方法中的关键组件，它的目标是促进跨语言和开发工具之间的数据模型共享，特别是那些基于统一建模语言（UML）的项目。 XMI规范定义了如何将UML模型转换成XML格式，以便在不同的系统和工具之间进行标准化的交换。版本2.5.1提供了一系列机器可消费的规范文件，如XMI.xsd和XMI-model.xmi，这些文件确保了数据模型的结构一致性和互操作性。标准文档的网址为<http://www.omg.org/spec/XMI/2.5.1>，用户可以从这里获取完整的规格和示例。该规范包含了多个组织的版权声明，包括但不限于88Solutions、Adaptive、Atego、Ceira Technologies、Compuware Corporation、Data Access Technologies、DSTC、Gentleware、Hewlett-Packard、IBM、IONA、MetaMatrix、NASA、NoMagic、Object Management Group、Softeam、Sparx Systems Pty Ltd、Sun、Telelogic AB、Unisys等，这反映了XMI作为业界广泛认可和使用的标准化接口的重要性。使用本规范，开发者可以方便地将UML模型转换成XMI格式，以便在分析、设计、构建和测试过程中与他人协作，或是与不同工具链集成，从而提高软件开发的效率和一致性。XMI的普及对于支持MDA方法论，推动软件开发的模型驱动实践，以及跨工具间模型复用具有深远的影响。遵循XMI 2.5.1，开发者需要了解如何正确解析和生成XMI文件，包括模型元素的命名空间、关系表示、以及可能的扩展机制。同时，也要注意遵守版权规定，确保在使用时尊重各组织的知识产权。随着软件工程领域对模型驱动开发的重视，XMI将继续发挥其核心作用，助力软件质量的提升和复杂系统的管理。

6 XML Metadata Interchange (XMI), v2.5.1

7.2.1 XML Validation of XMI documents

XML validation can determine whether the XML elements required by this International Standard are present in the XML

document containing model data, whether XML attributes that are required in these XML elements have values for them,

and whether some of the values are correct.

XML validation can also perform some verification that the model data conforms to a model. Although some checking

can be done, it is impossible to rely solely on XML validation to verify that the information transferred satisfies all of a

model’s semantic constraints. Complete verification cannot be done through XML validation because it is not currently

possible to specify all of the semantic constraints for a model in an XML schema, and the rules for automatic generation

of a schema preclude the use of semantic constraints that could be encoded in a schema manually, but cannot be

automatically encoded.

Finally, XML validation can be used to validate extensions to the model, because extensions must be represented as

elements; if those elements are defined in a schema, the schema can be used to verify the elements.

7.2.2 Requirements for XMI Schemas

Each schema used by XMI must satisfy the following requirements:

• All XML elements and attributes defined by the XMI specification must be imported in the schema. They cannot be put

directly in the schema itself, since there is only one target namespace per schema.

• Model constructs have corresponding element declarations, and may have an XML attribute declaration, as described

below. In addition, some constructs also have a complexType declaration. The declarations may utilize groups, attribute

groups, and types, as described below.

• Any XML elements that represent extensions to the model may be declared in a schema, although it is not necessary to

do so.

By default, XMI schemas allow incomplete metadata to be transmitted, but you can enforce the lower bound of

multiplicities if you wish. See 7.9 for further details.

7.3 Basic Principles

This sub clause discusses the basic organization of an XML schema for XMI. Detailed information about each of these

topics is included later in this chapter.

7.3.1 Required XML Declarations

This International Standard requires that XML element declarations, types, attributes, and attribute groups be included in

schemas to enable XML validation of metadata that conforms to this International Standard.

All XML elements defined by this International Standard are in the namespace “http://www.omg.org/spec/XMI/version-

namespace,” where version-namespace is the version of the XMI specification being used. The XML namespace

mechanism can be used to avoid name conflicts between the XMI elements and the XML elements from your MOF

models.

XML Metadata Interchange (XMI), v2.5.1 7

In addition to required XML element declarations, there are some attributes that must be defined according to this

International Standard. Every XML element that corresponds to a model class must have XML attributes that enable the

XML element to act as a proxy for a local or remote XML element. These attributes are used to associate an XML

element with another XML element. There are also other required attributes to let you put data in XML attributes rather

than XML elements. You may customize the declarations using MOF tag values.

7.3.2 Model Class Representation

Every model class is represented in the schema by an XML element whose name is the class name, as well as a

complexType whose name is the class name. The declaration of the type lists the properties of the class. By default, the

content models of XML elements corresponding to model classes do not impose an order on the properties.

By default, XMI allows you to serialize features using either XML elements or XML attributes; however, XMI allows you

to specify how to serialize them if you wish. Composite and multivalued properties are always serialized using XML

elements.

7.3.3 Model Extension Mechanism

Every XMI schema contains a mechanism for extending a model class. Zero or more extension elements are included in

the content model of each class. These extension elements have a content model of ANY, allowing considerable freedom

in the nature of the extensions. The processContents attribute is lax, which means that processors will validate the

elements in the extension if a schema is available for them, but will not report an error if there is no schema for them. In

addition, the top level XMI element may contain zero or more extension elements, which provides for the inclusion of

any new information. One use of the extension mechanism might be to transmit data that represents extensions to a

model.

Tools that rely on XMI are expected to store the extension information and export it again to enable round trip

engineering, even though it is unlikely they will be able to process it further. XML elements that are put in the extension

elements may be declared in schemas, but are not required to be.

7.4 XMI Schema and Document Structure

Every XMI schema consists of the following declarations:

• An XML version processing instruction. Example: <?XML version=”1.0”?>

• An optional encoding declaration that specifies the character set, which follows the ISO-10646 (also called extended

Unicode) standard. Example: <?XML version=”1.0” ENCODING=”UCS-2”?>

• Any other valid XML processing instructions.

• A schema XML element.

• An import XML element for the XMI namespace.

• Declarations for a specific model.

Every XMI document consists of the following declarations, unless the XMI is embedded in another XML document:

• An XML version processing instruction.

8 XML Metadata Interchange (XMI), v2.5.1

• An optional encoding declaration that specifies the character set.

• Any other valid XML processing instructions.

XMI imposes no ordering requirements beyond those defined by XML. XML Namespaces may also be declared in the

XMI element as described below.

The top element of the XMI information structure is either the XMI element, or an XML element corresponding to an

instance of a class in the MOF model. An XML document containing only XMI information will have XMI as the root

element of the document. It is possible for future XML exchange formats to be developed that extend XMI and embed

XMI elements within their XML elements.

7.5 XMI Model

This sub clause describes the model for XMI document structure, called the XMI model. The XMI model is an instance

of MOF for describing the XMI-specific information in an XMI document, such as the version, documentation,

extensions, and differences.

Using an XMI model enables XMI document metadata to be treated in the same fashion as other MOF metadata, allowing

use of standard MOF APIs for access to and construction of XMI-specific information in the same manner as other MOF

objects. A valid XMI document may contain XMI metadata but is not required to.

7.5.1 XML Schema for the XMI Model

When the XMI model is generated as an XML Schema following the XMI schema production rules, the result is a set of

XML element and attribute declarations. These declarations are shown in Clause 7 and given the XML namespace name

of the form “http://www.omg.org/spec/XMI/version-namespace,” where version-namespace is the XML namespace for

the version of the XMI specification being used. Every XMI-compliant schema must include the declarations of the

following XML elements by importing the declarations in the XMI namespace “http://www.omg.org/spec/XMI/version-

namespace.” The version of this XMI specification is 2.4.1, and its XMI namespace is “http://www.omg.org/spec/XMI/

20110701,” and the XSD file can be found at “http://www.omg.org/spec/XMI/20110701/XMI.xsd.”

In addition, there are attribute declarations and attributeGroup declarations that must be imported. These include the id

attribute, and the IdentityAttribs, LinkAttribs, and ObjectAttribs attribute groups. These constructs are not defined in the

XMI model.

In the declarations that follow, the XML Schema namespace, whose URI is “http://www.w3.org/2001/XMLSchema,” has

the namespace prefix “xsd.” The XMI namespace is the default namespace.

7.5.2 XMI Model classes

There are three diagrams that describe the XMI model. The details of the classes are described in the sub clauses below.

This sub clause gives an overview of the model.

Figure 7.1 shows the XMI element, documentation, and extension elements. The XMI class is an overall default container

for XMI document metadata and contents. The attributes of the XMI class are the documentation, differences (add,

replace, delete in Figure 7.2), and extensions. The Documentation class contains many fields to describe the document for

non-computational purposes. The Extension class contains the metadata for external information. The String datatype and

10 XML Metadata Interchange (XMI), v2.5.1

7.5.3 XMI

The root level XML element for XMI documents containing only XMI data may be the XMI element, but it must be the

XMI element if there are multiple elements. Its declaration is:

<xsd:complexType name="XMI">

<xsd:choice minOccurs="0" maxOccurs="unbounded">

<xsd:any processContents="strict"/>

</xsd:choice>

</xsd:complexType>

<xsd:element name="documentation" type="Documentation"/>

<xsd:element name="difference" type="Difference"/>

<xsd:element name="extension" type="Extension"/>

<xsd:element name="XMI" type="XMI"/>

Note that in the schema that the elements for documentation, difference and extension may not validly be included in the

xsd:choice for XMI since that already has xsd:any. However are the elements that must be used within the XMI elements.

The Documentation, Difference, and Extension elements (starting with uppercase), defined in the following sub clauses,

may only be used if they are root elements, not nested underneath XMI, and qualified with the XMI namespace: for

example xmi:Documentation.

Each version of XMI is unambiguously identified by its unique namespace URI of the form “http://www.omg.org/spec/

XMI/version-namespace.”

The XMI element need not be the root element of an XML document; you can include it inside any XML element that

was not serialized according to this International Standard. If a document contains only XMI information, the XMI

element may not be present when there is only a single top-level object, but is often useful for consistency and for

elements such as Documentation. The start of XMI information and identification of the XMI version is indicated by the

presence of the XMI namespace declaration, regardless of whether the XMI element itself is present. Clause 8 contains

examples of the use of the XMI element.

The XMI class has the XMI tag org.omg.xmi.contentType set to “any” to indicate that any XMI element may be present

in the XMI stream.

See “Overall Document Structure” on page 60” for details on how the XMI class is serialized.

The XMI model package has the following tag settings:

• tag org.omg.xmi.nsURI set to “http://www.omg.org/spec/XMI/version-namespace”

• tag org.omg.xmi.nsPrefix set to “xmi”

• tag org.omg.xmi.superClassFirst set to “true”

• tag org.omg.xmi.useSchemaExtension set to “true”

• tag org.omg.xmi.element set to “true”

• tag org.omg.xmi.attribute set to “false”

7.5.4 Extension

The Extension class is designed to contain extended information outside the scope of the user model. Extensions are a

multivalued attribute of the XMI class and may also be embedded in specific locations in an XMI document. The Schema

for extension is:

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