These are the types that other types are based on. The simpleTypes are 'abstract' in the sense that they are not intended to be used directly except as the restriction/extension base of another type. The intent is to control facets of simple types at a high level. These types specify the maximum size that should be assumed for interoperability between different schemas. A specialized schema that represents a controlled data source may utilize a smaller size but more generalized schemas which may have many data sources should probably retain these sizes. Suffixes (e.g., "String", "Count", "Enum") are used to more easily distinguish the data concept that underlies the type. Unbounded types such as the following should not be used without size/length constraints. xsd:string xsd:decimal (use float or double instead) xsd:hexBinary xsd:base64Binary xsd:anyURI xsd:QName xsd:NOTATION xsd:normalizedString xsd:token xsd:language xsd:NMTOKEN xsd:NMTOKENS xsd:Name xsd:NCName xsd:ID xsd:IDREF xsd:IDREFS xsd:ENTITY xsd:ENTITIES xsd:integer (use long, int, short or byte instead) xsd:nonPositiveInteger xsd:negativeInteger xsd:nonNegativeInteger xsd:positiveInteger Bounded types such as the following can be used without constraints: xsd:boolean xsd:float xsd:double xsd:duration xsd:dateTime xsd:time xsd:date xsd:gYearMonth xsd:gYear xsd:gMonthDay xsd:gDay xsd:gMonth xsd:long xsd:int xsd:short xsd:byte xsd:unsignedLong xsd:unsignedInt xsd:unsignedShort xsd:unsignedByte The intended abstract supertype of all 'anyURI' types. This type allows all values of an anyURI to be constrained to a maximum length. This type should not be used directly except to derive another type. This length should allow the value to be mapped to either a fixed length or a variable length character type in commonly used DBMSs. The empty string is not allowed. The intended abstract supertype of all enumerated short "codes". This abstract type allows the maximum length of a code enumeration to be centrally defined. This type should not be used directly except to derive another type. It should be used for uncontrolled strings which are candidates to become enumerations at a future date. The intended abstract supertype of all user assigned human recognizable contexual identifier of something. There should be no assumption that (interoperable) semantic information will be extracted from the identifier by a third party. This type of value is intended to be unique (e.g., via key and keyref) and is not a candidate to be constrained to an enumerated list. A user assigned human recognizable contexual identifier of something. There should be no assumption that (interoperable) semantic information will be extracted from the identifier by a third party. This type of value is intended to be unique (e.g., via key and keyref) and is not a candidate to be constrained to an enumerated list. A community assigned human recognizable short name. This type of value is intended to be unique and is generally a candidate to be constrained to an enumerated list. A Universal Resource Identifier. This includes URLs.