Clarify Data Types

[benajamin]

We have not specified precisely what NX_NUMBER incudes, e.g. does it include NX_QUATERNION?
Further, issue nexusformat/definitions#945 requires a data type that encompasses both NX_NUMBER and NX_CHAR.

[benajamin]

Proposal is to define NX_CHAR_XOR_NUM which encompasses NX_NUMBER and NX_CHAR such that either type can be used exclusively for all elements of the entire dataset.

[benajamin]

Proposal is to replace the description of NX_NUMBER in the NeXus manual with: "any of the set of non-compound number representations NX_INT, NX_UINT, NX_POSINT and NX_FLOAT."

[benajamin]

and for completeness:
Proposal is to define NX_COMPOUND as encompassing the set of compound number types such as NX_COMPLEX, NX_CCOMPLEX, NX_PCOMPLEX and NX_QUATERNION

[prjemian]

NX_NUMBER is not vague:

	<xs:simpleType name="NX_NUMBER">
		<xs:annotation>
			<xs:documentation>any valid NeXus number representation</xs:documentation>
		</xs:annotation>
		<xs:union memberTypes="
			nxdl:NX_INT 
			nxdl:NX_UINT 
			nxdl:NX_POSINT 
			nxdl:NX_FLOAT
			" />
	</xs:simpleType>

[FreddieAkeroyd]

NX_ALPHANUM to me usually means a string of numbers and characters, how about NX_SIMPLETYPE ? or just NX_SIMPLE to complement NX_COMPOUND

[prjemian]

simpleType is an XSD/XML thing, seems awkward

[prjemian]

NX_CHAR_OR_NUM

[prjemian]

NX_CHAR_XOR_NUM

[PeterC-DLS]

and for completeness: Proposal is to define NX_COMPOUND as encompassing the set of compound number types such as NX_COMPLEX, NX_CCOMPLEX, NX_PCOMPLEX and NX_QUATERNION

Rejected as a use-case cannot be forseen without including simple number types (i.e. NX_NUMBER).