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Mapping Common Data Formats

Root Element

The UML Class Model is a graph data structure. However, the two supported implementation formats (JSON and XML) are hierarchical (also called a tree). All hierarchies must start with a root, which is indicated in the UML model as a class stereotyped with «root».

Data Type Mapping

The UML model uses a number of primitive and specialized types based on the XML Schema.

UML	XML	JSON	JSON Format
String	xsd:string	String
date	xsd:date	String	date
boolean	xsd:boolean	Boolean
base64Binary	xsd:base64Binary	String	byte
anyURI	xsd:anyURI	String	uri
float	xsd:float	number

Representing multiplicities

Some attributes in the UML model can repeat. Repetition is represented by multiplicities whose lower or upper cardinality is greater than one. For example, 1..2, 2..4, 0..*, etc.

An asterisk for the upper cardinality represents an unbounded number of repetitions.

Multiplicities in XML

UML attributes with multiplicities greater than one are represented in XML as repeating elements.

Example:

<n1:Uri Annotation="mobile">http://mobile.samplesite.com/</n1:Uri>
<n1:Uri Annotation="desktop">http://www.samplesite.com/</n1:Uri>

Multiplicities in JSON

UML attributes with multiplicities greater than one are represented in JSON as an array of objects.

Example:

"Uri":
    [
        {
            "@type": "ElectionResults.AnnotatedUri",
            "Annotation": "mobile",
            "Content": "http://mobile.samplesite.com/"
        },
        {
            "@type": "ElectionResults.AnnotatedUri",
            "Annotation": "desktop",
            "Content": "http://www.samplesite.com/"
        }
    ]

Even if implementer wants to provide a single occurrence of an attribute, it must be wrapped in an array.

Example:

"Uri":
    [
        {
            "@type": "ElectionResults.AnnotatedUri",
            "Annotation": "mobile",
            "Content": "http://mobile.samplesite.com/"
        }
    ]

Pointers

Some classes of data may be referenced again and again, for example political parties or geopolitical units. It would make sense to put instances of these classes in single location and reference them whenever they need to be used.

The CDF model represents these pointers as directed associations between classes.

XML Pointers

XML provide two built in types for handling pointers, one for establishing the reusable element (xsd:ID) and one for referring to it (xsd:IDREF).

Example:

Here we define a reusable ReportingUnit that is referenced by multiple Contests.

{
	"@type": "ElectionResults.ElectionReport",
	"Election": [
		{
			"@type": "ElectionResults.Election",
			"Contest": [
				{
					"@id": "cc-sc-sherif",
					"@type": "ElectionResults.CandidateContest",
					"ElectoralDistrict": "gp-summit-county",
					"Name": "Summit County Sherif"
				},
				{
					"@id": "cc-sc-fiscal-officer",
					"@type": "ElectionResults.CandidateContest",
					"ElectoralDistrict": "gp-summit-county",
					"Name": "Summit County Fiscal Officer"
				}
			],
			"Type": "general"
		}
	],
	"GpUnit": [
		{
			"@id": "gp-summit-county",
			"@type": "ElectionResults.ReportingUnit",
			"Name": "Summit County"
		}
	]
}

Figure: Example of pointers in JSON

<ElectionReport>
	<Election>
		<Contest ObjectId="cc-sc-sherif" xsi:type="CandidateContest">
			<ElectoralDistrictId>gp-summit-county</ElectoralDistrictId>
			<Name>Summit County Sherif</Name>
		</Contest>
		<Contest ObjectId="cc-sc-fiscal-officer" xsi:type="CandidateContest">
			<ElectoralDistrictId>gp-summit-county</ElectoralDistrictId>
			<Name>Summit County Fiscal Officer</Name>
		</Contest>
		<ElectionScopeId>gp-summit-county</ElectionScopeId>
		<Type>general</Type>
	</Election>
	<GpUnit ObjectId="gp-summit-county">
		<Name>Summit County</Name>
	</GpUnit>
</ElectionReport>

XML specific notes

Elements and Attributes

XML provides two data structures for presenting data, attributes and elements. Attributes are typically used for metadata, while elements are used for the class' primary data.

UML and JSON only provide a single data structure for presenting information, attributes (UML) and objects (JSON), respectively.

Attributes of the UML Model are transformed into XML elements, unless the UML attribute has the «xmlAttribute» stereotype or the class contains an attribute with the «simpleContent» stereotype (see below).

Simple Content

Some classes in the UML model may have an attribute with the «simpleType» stereotype applied. This stereotype indicates that the attribute is the target for the character data of the XML element. All other UML attributes will be transformed into XML attributes.

Example:

File
«simpleContent»-Data : base64Binary [1]
-fileName : string [0..1]
-mimeType : string [0..1]

Table: UML Class File

<n2:FileValue fileName="String" mimeType="String">UjBsR09EbGhjZ0dTQUxNQUFBUUNBRU1tQ1p0dU1GUXhEUzhi</n2:FileValue>