Base Type
Base Type is an entity similar to the data types in most programming languages. It specifies the kind of value a property can contain - its atomic type. MDDL defines the following base types:

Boolean:
The base type Boolean is similar to the data type Boolean in programming languages where the values are limited to the logical values "true"(1) and "false"(0). It is defined by the W3C XML Schema type xsd:Boolean and is constrained by that definition. The properties belonging to the base type Boolean are represented using the element mdBoolean.

DateTime:
The base type dateTime holds date, time or both. It is constrained by the union of the W3C XML Schema types xsd:dateTime, xsd:date, and xsd:time. The properties belonging to the base type dateTime are represented using the element mdDateTime.

Decimal:
The base type Decimal holds the numeric data. It is defined by the W3C XML Schema type xsd:decimal and is constrained by that definition. The properties belonging to the base type decimal are represented using the element mdDecimal.

Duration:
The base type Duration is used to represent a period of time. It is defined by the W3C XML Schema type xsd:duration and is constrained by that definition. The properties belonging to the base type duration are represented using the element mdDuration. Note that duration is a key component of the MDDL property 'period' which permits specification of a start, end, and duration, or any combination thereof.

Enumeration:
The base type Enumeration is a subset of base type string. The properties of type Enumeration are represented by the element mdString and include a special 'scheme' attribute to reference codes from controlled vocabularies.

NonNegativeDecimal:
The base type NonNegativeDecimal holds values of 0 or greater (similar to a Decimal). Note: At this time it is not constrained to non-negative values although it should only be used where non-negative values are expected.

String:
The base type String holds all the string-based data. It is defined by the W3C XML Schema type xsd:string and is constrained by that definition. The properties belonging to the base type string are represented using the element mdString.

URI:
The base type URI holds Uniform Resource Identifiers such as web address (URLs). It can also be used to hold XPath references as necessary. It is defined by the W3C XML Schema type xsd:anyURI and is constrained by that definition. The properties belonging to this base type are represented using the element mdURI.

Adding Types It is not recommended that any other base types be added outside the formal specification review process. These base types are fundamental to the recipient’ s understanding and processing of the data. All requests for modifications or new base types should be directed to the MDDL sponsoring agency.