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source: trunk/nxdl.xsd @ 1089

Revision 1060, 49.7 KB checked in by Pete Jemian, 3 months ago (diff)
fixes #216 (updated copyrights to 2012, renamed all to NIAC ownership
Property svn:eol-style set to `native` Property svn:keywords set to `Date Revision Author HeadURL Id`

Line
1	<?xml version="1.0" encoding="UTF-8"?>
2	<!--
3	########### SVN repository information ###################
4	# $LastChangedDate$
5	# $LastChangedBy$
6	# $LastChangedRevision$
7	# $HeadURL$
8	########### SVN repository information ###################
9	-->
10
11	<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
12	targetNamespace="http://definition.nexusformat.org/nxdl/@NXDL_RELEASE@"
13	xmlns:nx="http://definition.nexusformat.org/nxdl/@NXDL_RELEASE@"
14	version="$Id$"
15	xmlns:db="http://docbook.org/ns/docbook"
16	elementFormDefault="qualified">
17
18	<xs:annotation>
19	<xs:documentation>
20	# NeXus - Neutron and X-ray Common Data Format
21	#
22	# Copyright (C) 2008-2012 NeXus International Advisory Committee (NIAC)
23	#
24	# This library is free software; you can redistribute it and/or
25	# modify it under the terms of the GNU Lesser General Public
26	# License as published by the Free Software Foundation; either
27	# version 3 of the License, or (at your option) any later version.
28	#
29	# This library is distributed in the hope that it will be useful,
30	# but WITHOUT ANY WARRANTY; without even the implied warranty of
31	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
32	# Lesser General Public License for more details.
33	#
34	# You should have received a copy of the GNU Lesser General Public
35	# License along with this library; if not, write to the Free Software
36	# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
37	#
38	# For further information, see http://www.nexusformat.org
39	</xs:documentation>
40	</xs:annotation>
41
42	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
43
44	<xs:include schemaLocation="nxdlTypes.xsd">
45	<xs:annotation>
46	<xs:documentation>
47	Definitions of the basic data types and unit types
48	allowed in NXDL instance files.
49	</xs:documentation>
50	</xs:annotation>
51	</xs:include>
52
53	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
54
55	<!-- define the document root element -->
56	<xs:element name="definition" type="nx:definitionType">
57	<xs:annotation>
58	<xs:documentation>
59	A <db:code>definition</db:code> element
60	is the <db:code>group</db:code> at the
61	root of every NXDL specification.
62	It may <db:emphasis>only</db:emphasis> appear
63	at the root of an NXDL file and must only appear
64	<db:emphasis role="bold">once</db:emphasis>
65	for the NXDL to be <db:emphasis>well-formed</db:emphasis>.
66	</xs:documentation>
67	</xs:annotation>
68	</xs:element>
69
70	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
71
72	<xs:simpleType name="validItemName">
73	<xs:annotation>
74	<xs:documentation>
75	Used for allowed names of elements and attributes.
76	Need to be restricted to valid program variable names.
77	Note: This means no "-" or "." characters can be allowed and
78	you cannot start with a number.
79	HDF4 had a 64 character limit on names
80	(possibly including NULL) and NeXus enforces this
81	via the <db:code>NX_MAXNAMELEN</db:code> variable with
82	a <db:emphasis role="bold">64</db:emphasis> character limit (which
83	may be 63 on a practical basis if one considers a NULL
84	terminating byte).
85	(This data type is used internally in the NXDL schema
86	to define a data type.)
87	</xs:documentation>
88	</xs:annotation>
89	<xs:restriction base="xs:token">
90	<xs:pattern value="[A-Za-z_][\w_]*" />
91	<xs:maxLength value="63" /> <!-- enforce via NX_MAXNAMELEN -->
92	</xs:restriction>
93	</xs:simpleType>
94
95	<xs:simpleType name="validNXClassName">
96	<xs:annotation>
97	<xs:documentation>
98	Used for allowed names of NX class types (e.g. NXdetector)
99	not the instance (e.g. bank1) which is covered by validItemName.
100	(This data type is used internally in the NXDL schema
101	to define a data type.)
102	</xs:documentation>
103	</xs:annotation>
104	<xs:restriction base="nx:validItemName">
105	<xs:pattern value="NX.+"/>
106	</xs:restriction>
107	</xs:simpleType>
108
109	<xs:simpleType name="validTargetName">
110	<xs:annotation>
111	<xs:documentation>
112	This is a valid link target - currently it must be an absolute path
113	made up of valid names with the <db:code>/</db:code> character delimiter. But we may
114	want to consider allowing "<db:code>..</db:code>" (parent of directory) at some point.
115	If the <db:code>name</db:code> attribute is helpful, then use it in the path
116	with the syntax of "<db:code>name:type</db:code>" as in these examples:
117	<db:programlisting language="c"
118	>/NXentry/NXinstrument/analyzer:NXcrystal/ef
119	/NXentry/NXinstrument/monochromator:NXcrystal/ei
120	/NX_other</db:programlisting>
121	Must also consider use of <db:code>name</db:code> attribute in resolving <db:code>link</db:code> targets.
122	(This data type is used internally in the NXDL schema
123	to define a data type.)
124	</xs:documentation>
125	</xs:annotation>
126	<xs:restriction base="xs:token">
127	<xs:annotation>
128	<xs:documentation>
129	The HDF5 documentation
130	(<db:uri>http://www.hdfgroup.org/HDF5/doc/UG/UG_frame09Groups.html</db:uri>)
131	says "<db:quote>Note that relative path names in HDF5 do not employ the ../ notation,
132	the UNIX notation indicating a parent directory, to indicate a parent group.</db:quote>"
133	Thus, if we only consider the case of
134	<db:code>[name:]type</db:code>, the matching regular expression syntax
135	is written: <db:code>/[a-zA-Z_][\w_](:[a-zA-Z_][\w_])?)+</db:code>.
136	Note that HDF5 also permits relative path names, such as:
137	<db:code>GroupA/GroupB/Dataset1</db:code>
138	but this is not permitted in the matching regular expression and not supported in NAPI.
139	</xs:documentation>
140	</xs:annotation>
141	<xs:pattern value="(/[a-zA-Z_][\w_](:[a-zA-Z_][\w_])?)+" />
142	</xs:restriction>
143	</xs:simpleType>
144
145	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
146
147	<xs:complexType name="definitionType">
148	<xs:annotation>
149	<xs:documentation>
150	A <db:code>definition</db:code> is the root element of every NXDL definition.
151	The <db:code>definitionType</db:code> defines the documentation,
152	attributes, fields, and groups that will be used
153	as children of the <db:code>definition</db:code> element.
154	Could contain these elements:
155	<db:itemizedlist>
156	<db:listitem><db:para><db:code>attribute</db:code></db:para></db:listitem>
157	<db:listitem><db:para><db:code>doc</db:code></db:para></db:listitem>
158	<db:listitem><db:para><db:code>field</db:code></db:para></db:listitem>
159	<db:listitem><db:para><db:code>group</db:code></db:para></db:listitem>
160	<db:listitem><db:para><db:code>link</db:code></db:para></db:listitem>
161	</db:itemizedlist>
162	Note that a <db:code>definition</db:code> element also includes the definitions of the
163	<db:code>basicComponent</db:code> data type.
164	(The <db:code>definitionType</db:code> data type is used internally in the NXDL schema
165	to define elements and attributes to be used by users in NXDL specifications.)
166	</xs:documentation>
167	</xs:annotation>
168	<xs:sequence>
169	<xs:element name="symbols" type="nx:symbolsType" minOccurs="0" maxOccurs="1">
170	<xs:annotation>
171	<xs:documentation>
172	Use the <db:code>symbols</db:code> element to create a list of
173	<db:code>symbol</db:code>s to define each of the mnemonics that
174	represent the length of each dimension in a vector or array.
175	</xs:documentation>
176	</xs:annotation>
177	</xs:element>
178	<xs:group ref="nx:groupGroup" minOccurs="0" maxOccurs="unbounded">
179	<xs:annotation>
180	<xs:documentation>
181	In addition to an optional <db:code>symbols</db:code> list,
182	a <db:code>definition</db:code> may contain any of the items
183	allowed in a <db:code>group</db:code>.
184	</xs:documentation>
185	</xs:annotation>
186	</xs:group>
187	</xs:sequence>
188	<xs:attribute name="name" use="required" type="nx:validItemName">
189	<xs:annotation>
190	<xs:documentation>
191	(<db:emphasis role="bold">required</db:emphasis>)
192	The <db:code>name</db:code> of this NXDL file (without the file extensions).
193	The name must be unique amongst all the NeXus base class, application,
194	and contributed definitions. For the class to be adopted by the NIAC,
195	the first two letters must be "<db:code>NX</db:code>" (in uppercase). Any other use
196	must <db:emphasis>not</db:emphasis> begin with "<db:code>NX</db:code>" in any combination
197	of upper or lower case.
198	</xs:documentation>
199	</xs:annotation>
200	</xs:attribute>
201	<xs:attribute name="version" use="required">
202	<xs:annotation>
203	<xs:documentation>
204	(<db:emphasis role="bold">required</db:emphasis>)
205	Version of <db:emphasis>this</db:emphasis> NXDL definition.
206	Each NXDL specification
207	may have a different version to facilitate software maintenance.
208	This value is modified by the person who edits this file when
209	this NXDL specification has changed significantly (in a way that
210	downstream software should be aware).
211	</xs:documentation>
212	</xs:annotation>
213	</xs:attribute>
214	<xs:attribute name="type" use="required" type="nx:definitionTypeAttr">
215	<xs:annotation>
216	<xs:documentation>
217	(<db:emphasis role="bold">required</db:emphasis>)
218	Must be <db:code>type="group"</db:code>
219	</xs:documentation>
220	</xs:annotation>
221	</xs:attribute>
222	<xs:attribute name="extends" use="optional">
223	<xs:annotation>
224	<xs:documentation>
225	The <db:code>extends</db:code> attribute allows this definition
226	to <db:emphasis>subclass</db:emphasis> from another NXDL,
227	otherwise <db:code>extends="NXobject"</db:code> should be used.
228	</xs:documentation>
229	</xs:annotation>
230	</xs:attribute>
231	<xs:attribute name="restricts" use="optional">
232	<xs:annotation>
233	<xs:documentation>
234	The <db:code>restricts</db:code> attribute is a flag to the data validation.
235	When <db:code>restricts="1"</db:code>, any non-standard component found
236	(and checked for validity aginst this NXDL specification)
237	in a NeXus data file will be flagged as an error. If the
238	<db:code>restricts</db:code> attribute is not present, any such situations
239	will produce a warning.
240	</xs:documentation>
241	</xs:annotation>
242	</xs:attribute>
243	<xs:attribute name="svnid" use="optional">
244	<xs:annotation>
245	<xs:documentation>
246	The identifier string from the subversion revision control system.
247	This reports the time stamp and the revision number of this file.
248	(Updated automatically, unlike the <db:code>version</db:code> attribute.)
249	</xs:documentation>
250	</xs:annotation>
251	</xs:attribute>
252	<xs:attribute name="category" use="required">
253	<xs:annotation>
254	<xs:documentation>
255	NXDL <db:code>base</db:code> definitions define the dictionary
256	of terms to use for these components.
257	All terms in a <db:code>base</db:code> definition are optional.
258	NXDL <db:code>application</db:code> definitions define what is
259	required for a scientific interest.
260	All terms in an <db:code>application</db:code> definition
261	are required.
262	NXDL <db:code>contributed</db:code> definitions may be
263	considered either base or applications.
264	Contributed definitions <emphasis>must</emphasis> indicate
265	their intended use, either as a base class or
266	as an application definition.
267	</xs:documentation>
268	</xs:annotation>
269	<xs:simpleType>
270	<xs:restriction base="xs:string">
271	<xs:enumeration value="base"/>
272	<xs:enumeration value="application"/>
273	<xs:enumeration value="contributed"/>
274	</xs:restriction>
275	</xs:simpleType>
276	</xs:attribute>
277	<xs:attribute name="ignoreExtraGroups" use="optional" type="nx:NX_BOOLEAN" default="false">
278	<xs:annotation>
279	<xs:documentation>
280	Only validate known groups; do not not warn about unknowns.
281	The <db:code>ignoreExtraGroups</db:code> attribute is a flag to the process of
282	validating NeXus data files. By setting <db:code>ignoreExtraGroups="true"</db:code>,
283	presence of any undefined groups in this class will not generate warnings
284	during validation. Normally, validation will check all the groups against
285	their definition in the NeXus base classes and
286	application definitions. Any items found that do not match the definition
287	in the NXDL will generate a warning message.
288	<db:emphasis>The <db:code>ignoreExtraGroups</db:code> attribute
289	should be used sparingly!</db:emphasis>
290	</xs:documentation>
291	</xs:annotation>
292	</xs:attribute>
293	<xs:attribute name="ignoreExtraFields" use="optional" type="nx:NX_BOOLEAN" default="false">
294	<xs:annotation>
295	<xs:documentation>
296	Only validate known fields; do not not warn about unknowns.
297	The <db:code>ignoreExtraFields</db:code> attribute is a flag to the process of
298	validating NeXus data files. By setting <db:code>ignoreExtraFields="true"</db:code>,
299	presence of any undefined fields in this class will not generate warnings
300	during validation. Normally, validation will check all the fields against
301	their definition in the NeXus base classes and
302	application definitions. Any items found that do not match the definition
303	in the NXDL will generate a warning message.
304	<db:emphasis>The <db:code>ignoreExtraFields</db:code> attribute should be used sparingly!</db:emphasis>
305	</xs:documentation>
306	</xs:annotation>
307	</xs:attribute>
308	<xs:attribute name="ignoreExtraAttributes" use="optional" type="nx:NX_BOOLEAN" default="false">
309	<xs:annotation>
310	<xs:documentation>
311	Only validate known attributes; do not not warn about unknowns.
312	The <db:code>ignoreExtraAttributes</db:code> attribute is a flag to the process of
313	validating NeXus data files. By setting <db:code>ignoreExtraAttributes="true"</db:code>,
314	presence of any undefined attributes in this class will not generate warnings
315	during validation. Normally, validation will check all the attributes
316	against their definition in the NeXus base classes and
317	application definitions. Any items found that do not match the definition
318	in the NXDL will generate a warning message.
319	<db:emphasis>The <db:code>ignoreExtraAttributes</db:code> attribute should be used sparingly!</db:emphasis>
320	</xs:documentation>
321	</xs:annotation>
322	</xs:attribute>
323	</xs:complexType>
324
325	<xs:simpleType name="definitionTypeAttr">
326	<xs:annotation>
327	<xs:documentation>
328	Prescribes the allowed values for <db:code>definition</db:code> <db:code>type</db:code> attribute.
329	(This data type is used internally in the NXDL schema
330	to define a data type.)
331	</xs:documentation>
332	</xs:annotation>
333	<xs:restriction base="xs:string">
334	<xs:enumeration value="group" />
335	<xs:enumeration value="definition" />
336	</xs:restriction>
337	</xs:simpleType>
338
339	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
340
341	<xs:complexType name="groupType">
342	<xs:annotation>
343	<xs:documentation>
344	A group element refers to the definition of
345	an existing NX object or a locally-defined component.
346	Could contain these elements:
347	<db:itemizedlist>
348	<db:listitem><db:para><db:code>attribute</db:code></db:para></db:listitem>
349	<db:listitem><db:para><db:code>doc</db:code></db:para></db:listitem>
350	<db:listitem><db:para><db:code>field</db:code></db:para></db:listitem>
351	<db:listitem><db:para><db:code>group</db:code></db:para></db:listitem>
352	<db:listitem><db:para><db:code>link</db:code></db:para></db:listitem>
353	</db:itemizedlist>
354	Note that a <db:code>group</db:code> element also includes the definitions of the
355	<db:code>basicComponent</db:code> data type.
356	(The <db:code>groupType</db:code> data type is used internally in the NXDL schema
357	to define elements and attributes to be used by users in NXDL specifications.)
358	</xs:documentation>
359	</xs:annotation>
360	<xs:group ref="nx:groupGroup" minOccurs="0" maxOccurs="unbounded">
361	<xs:annotation>
362	<xs:documentation>
363	A <db:code>group</db:code> may contain other <db:code>group</db:code>s.
364	</xs:documentation>
365	</xs:annotation>
366	</xs:group>
367	<xs:attribute name="type" use="required" type="nx:validNXClassName">
368	<xs:annotation>
369	<xs:documentation>
370	The <db:code>type</db:code> attribute <db:emphasis>must</db:emphasis>
371	contain the name of a
372	NeXus base class, application definition, or contributed definition.
373	</xs:documentation>
374	</xs:annotation>
375	</xs:attribute>
376	<xs:attribute name="name" use="optional" type="nx:validItemName">
377	<xs:annotation>
378	<xs:documentation>
379	A particular scientific application may expect
380	a name of a <db:code>group</db:code> element. It is helpful but not
381	required to specify the <db:code>name</db:code>
382	attribute in the NXDL file.
383	It is suggested to always specify a <db:code>name</db:code>
384	to avoid ambiguity. It is also suggested to
385	derive the <db:code>name</db:code> from the
386	type, using an additional number suffix as necessary.
387	For example, consider a data file with only one
388	<db:code>NXentry</db:code>. The suggested default
389	<db:code>name</db:code> would
390	be <db:code>entry</db:code>. For a data file with two or more
391	<db:code>NXentry</db:code> groups, the suggested names would be
392	<db:code>entry1</db:code>, <db:code>entry2</db:code>, ...
393	Alternatively, a scientific application such as small-angle
394	scattering might require
395	a different naming procedure; two different <db:code>NXaperture</db:code> groups
396	might be given the names <db:code>beam-defining slit</db:code>
397	and <db:code>scatter slit</db:code>.
398	</xs:documentation>
399	</xs:annotation>
400	</xs:attribute>
401	<xs:attribute name="minOccurs" use="optional" default="0" type="xs:nonNegativeInteger">
402	<xs:annotation>
403	<xs:documentation>
404	Minimum number of times this <db:code>group</db:code> is allowed to be present within its
405	parent group. Note each <db:code>group</db:code> must have a <db:code>name</db:code> attribute
406	that is unique among all <db:code>group</db:code> and <db:code>field</db:code>
407	declarations within a common parent group.
408	</xs:documentation>
409	</xs:annotation>
410	</xs:attribute>
411	<xs:attribute name="maxOccurs" use="optional" default="unbounded">
412	<xs:annotation>
413	<xs:documentation>
414	Maximum number of times this <db:code>group</db:code> is allowed to be present within its
415	parent <db:code>group</db:code>. Note each <db:code>group</db:code> must have a <db:code>name</db:code> attribute
416	that is unique among all <db:code>group</db:code> and <db:code>field</db:code>
417	declarations within a common parent <db:code>group</db:code>.
418	</xs:documentation>
419	</xs:annotation>
420	</xs:attribute>
421	</xs:complexType>
422
423	<xs:group name="groupGroup">
424	<xs:annotation>
425	<xs:documentation>
426	A <db:code>groupGroup</db:code> defines the allowed children of a
427	<db:code>group</db:code> specification.
428	</xs:documentation>
429	</xs:annotation>
430	<xs:sequence>
431	<xs:element name="doc" type="nx:docType" minOccurs="0" maxOccurs="1">
432	<xs:annotation>
433	<xs:documentation>
434	Describe the purpose of this <db:code>group</db:code>.
435	This documentation will go into the manual.
436	</xs:documentation>
437	</xs:annotation>
438	</xs:element>
439	<xs:element name="attribute" type="nx:attributeType" minOccurs="0" maxOccurs="unbounded">
440	<xs:annotation>
441	<xs:documentation>
442	Use an <db:code>attribute</db:code> if additional information
443	needs to be associated with a <db:code>group</db:code>.
444	</xs:documentation>
445	</xs:annotation>
446	</xs:element>
447	<xs:element name="group" type="nx:groupType" minOccurs="0" maxOccurs="unbounded">
448	<xs:annotation>
449	<xs:documentation>
450	A <db:code>group</db:code> may contain <db:code>group</db:code>s.
451	</xs:documentation>
452	</xs:annotation>
453	</xs:element>
454	<xs:element name="field" type="nx:fieldType" minOccurs="0" maxOccurs="unbounded">
455	<xs:annotation>
456	<xs:documentation>
457	A <db:code>group</db:code> may contain <db:code>field</db:code>s (datasets).
458	</xs:documentation>
459	</xs:annotation>
460	</xs:element>
461	<xs:element name="link" type="nx:linkType" minOccurs="0" maxOccurs="unbounded">
462	<xs:annotation>
463	<xs:documentation>
464	Use a <db:code>link</db:code> to refer locally to
465	information placed elsewhere else in the data storage hierarchy.
466	The <db:code>name</db:code> attribute uniquely identifies
467	the element in this <db:code>group</db:code>.
468	The <db:code>target</db:code> attribute
469	(added automatically in a data file by the NAPI)
470	identifies the original location of this data in the
471	data storage hierarchy.
472	In an NXDL specification, the <db:code>target</db:code> attribute
473	indicates a link to be made by the software that writes the data file.
474	The value, as written in the NXDL file, will be a suggestion of
475	the path to the source of the link.
476	For example:
477	<db:programlisting language="xml"
478	><link name="data" target="/NXentry/NXinstrument/NXdetector/data" /></db:programlisting>
479	The value of <db:code>target</db:code> is written using
480	the NeXus class names since this is a suggestion and does not actually use
481	the element names from a particular data file.
482	</xs:documentation>
483	</xs:annotation>
484	</xs:element>
485	</xs:sequence>
486	</xs:group>
487
488	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
489
490	<xs:complexType name="basicComponent">
491	<xs:annotation>
492	<xs:documentation>
493	A <db:code>basicComponent</db:code> defines the allowed name
494	format and attributes common to all <db:code>field</db:code>
495	and <db:code>group</db:code> specifications.
496	(This data type is used internally in the NXDL schema
497	to define elements and attributes to be used by users in NXDL specifications.)
498	</xs:documentation>
499	</xs:annotation>
500	<xs:sequence>
501	<xs:element name="doc" type="nx:docType" minOccurs="0" maxOccurs="1">
502	<xs:annotation>
503	<xs:documentation>
504	Describe this <db:code>basicComponent</db:code> and its use.
505	This documentation will go into the manual.
506	</xs:documentation>
507	</xs:annotation>
508	</xs:element>
509	</xs:sequence>
510	<xs:attribute name="name" use="required" type="nx:validItemName">
511	<xs:annotation>
512	<xs:documentation>
513	The <db:code>name</db:code> attribute is the
514	identifier string for this entity.
515	It is required that <db:code>name</db:code> must be unique
516	within the enclosing <db:code>group</db:code>.
517	The rule (<db:code>validItemName</db:code>) is defined to only
518	allow names that can be represented as valid variable names
519	in most computer languages.
520	</xs:documentation>
521	</xs:annotation>
522	</xs:attribute>
523	<xs:attribute name="deprecated" use="optional">
524	<xs:annotation>
525	<xs:documentation>
526	The presence of the <db:code>deprecated</db:code> attribute
527	indicates to the data file validation process that
528	an advisory message (specified as the content of the
529	<db:code>deprecated</db:code> attribute) will be reported.
530	Future versions of the NXDL file might
531	not define (or even re-use) this component.
532	For example:
533	<db:programlisting language="c">deprecated="Should the 'deprecated' attribute become a 'field' in a future version?"</db:programlisting>
534	Note: because <db:code>deprecated</db:code> is an attribute,
535	the XML rules do not permit it to have any element content
536	such as DocBook markup.
537	</xs:documentation>
538	</xs:annotation>
539	<xs:simpleType>
540	<xs:restriction base="xs:string">
541	<xs:pattern value=".(\w+)." />
542	</xs:restriction>
543	</xs:simpleType>
544	</xs:attribute>
545	</xs:complexType>
546
547	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
548
549	<xs:complexType name="fieldType">
550	<xs:annotation>
551	<xs:documentation>
552	A <db:code>field</db:code> declares a new element in the component being defined.
553	A <db:code>field</db:code> is synonymous with the HDF4 SDS (Scientific Data Set) and
554	the HDF5 <db:emphasis>dataset</db:emphasis> terms.
555	Could contain these elements:
556	<db:itemizedlist>
557	<db:listitem><db:para><db:code>attribute</db:code></db:para></db:listitem>
558	<db:listitem><db:para><db:code>dimensions</db:code></db:para></db:listitem>
559	<db:listitem><db:para><db:code>doc</db:code></db:para></db:listitem>
560	<db:listitem><db:para><db:code>enumeration</db:code></db:para></db:listitem>
561	</db:itemizedlist>
562	Note that a <db:code>field</db:code> element also includes the definitions of the
563	<db:code>basicComponent</db:code> data type.
564	(The <db:code>fieldType</db:code> data type is used internally in the NXDL schema
565	to define elements and attributes to be used by users in NXDL specifications.)
566	</xs:documentation>
567	</xs:annotation>
568	<xs:complexContent>
569	<xs:extension base="nx:basicComponent">
570	<xs:sequence>
571	<xs:element name="dimensions" type="nx:dimensionsType" minOccurs="0" maxOccurs="1">
572	<xs:annotation>
573	<xs:documentation>dimensions of a data element
574	in a NeXus file</xs:documentation>
575	</xs:annotation>
576	</xs:element>
577	<xs:element name="attribute" type="nx:attributeType" minOccurs="0" maxOccurs="unbounded">
578	<xs:annotation>
579	<xs:documentation
580	>attributes to be used with this field</xs:documentation>
581	</xs:annotation>
582	</xs:element>
583	<xs:element name="enumeration" type="nx:enumerationType" minOccurs="0">
584	<xs:annotation>
585	<xs:documentation>A field can specify which
586	values are to be used</xs:documentation>
587	</xs:annotation>
588	</xs:element>
589	</xs:sequence>
590	<xs:attribute name="units" type="nx:anyUnitsAttr">
591	<xs:annotation>
592	<xs:documentation>
593	String describing the engineering units.
594	The string should be appropriate for the value
595	and should conform to the NeXus rules for units.
596	Conformance is not validated at this time.
597	</xs:documentation>
598	</xs:annotation>
599	</xs:attribute>
600	<xs:attribute name="long_name" type="nx:NX_CHAR">
601	<xs:annotation>
602	<xs:documentation>
603	Descriptive name for this field (may include whitespace and engineering units).
604	Often, the long_name (when defined) will be used as the axis label on a plot.
605	</xs:documentation>
606	</xs:annotation>
607	</xs:attribute>
608	<xs:attribute name="signal" type="nx:NX_POSINT">
609	<xs:annotation>
610	<xs:documentation>
611	Presence of the <db:code>signal</db:code> attribute means this field is an ordinate.
612
613	Integer marking this field as plottable data (ordinates).
614	The value indicates the priority of selection or interest.
615	Some facilities only use <db:code>signal="1"</db:code>
616	while others use <db:code>signal="2"</db:code> to indicate
617	plottable data of secondary interest.
618	Higher numbers are possible but not common
619	and interpretation is not standard.
620
621	A field with a <db:code>signal</db:code> attribute should not have an <db:code>axis</db:code> attribute.
622	</xs:documentation>
623	</xs:annotation>
624	</xs:attribute>
625	<xs:attribute name="axes" type="nx:NX_CHAR">
626	<xs:annotation>
627	<xs:documentation>
628	Presence of the <db:code>axes</db:code> attribute means this field is an ordinate.
629
630	This attribute contains a colon (or comma in legacy files) delimited list
631	of the names of independent axes when plotting this field.
632	Each name in this list must exist as a field in the same group.
633	<!-- perhaps even discourage use of square brackets in axes attribute? -->
634	(Optionally, the list can be enclosed by square brackets but this is not common.)
635	The regular expression for this rule is:
636	<db:programlisting language="c">[A-Za-z_][\w_]([ :][A-Za-z_][\w_])*</db:programlisting>
637	</xs:documentation>
638	</xs:annotation>
639	</xs:attribute>
640	<xs:attribute name="axis" type="nx:NX_POSINT">
641	<xs:annotation>
642	<xs:documentation>
643	NOTE: Use of this attribute is discouraged. It is for legacy support.
644	You should use the axes attribute instead.
645
646	Presence of the <db:code>axis</db:code> attribute means this field is an abcissa.
647
648	The attribute value is an integer indicating this
649	field as an axis that is part of the data set.
650	The data set is a field with the attribute
651	<db:code>signal="1"</db:code> in the same group.
652	The value can range from 1 up to the number of
653	independent axes (abcissae) in the data set.
654
655	A value of <db:code>axis="1</db:code>" indicates that this field
656	contains the data for the first independent axis.
657	For example, the X axis in an XY data set.
658
659	A value of <db:code>axis="2"</db:code> indicates that this field
660	contains the data for the second independent axis.
661	For example, the Y axis in a 2-D data set.
662
663	A value of <db:code>axis="3"</db:code> indicates that this field
664	contains the data for the third independent axis.
665	For example, the Z axis in a 3-D data set.
666
667	A field with an <db:code>axis</db:code> attribute should
668	not have a <db:code>signal</db:code> attribute.
669	</xs:documentation>
670	</xs:annotation>
671	</xs:attribute>
672	<xs:attribute name="primary" type="nx:NX_POSINT">
673	<xs:annotation>
674	<xs:documentation>
675	Integer indicating the priority of selection
676	of this field for plotting (or visualization) as an axis.
677
678	Presence of the <db:code>primary</db:code> attribute means this
679	field is an abcissa.
680	</xs:documentation>
681	</xs:annotation>
682	</xs:attribute>
683	<xs:attribute name="type" type="nx:NAPI" default="NX_CHAR">
684	<xs:annotation>
685	<xs:documentation>
686	Defines the type of the element as allowed by the NAPI (NeXus Application Programmer Interface).
687	See elsewhere for the complete list of allowed NAPI types.
688	</xs:documentation>
689	</xs:annotation>
690	</xs:attribute>
691	<xs:attribute name="minOccurs" use="optional" default="0" type="nx:nonNegativeUnbounded">
692	<xs:annotation>
693	<xs:documentation>
694	Defines the minimum number of times this element may be used. Its
695	value is confined to zero or greater. Must be less than or equal to
696	the value for the "maxOccurs" attribute.
697	A value of "unbounded" is allowed.
698	</xs:documentation>
699	</xs:annotation>
700	</xs:attribute>
701	<xs:attribute name="maxOccurs" use="optional" default="1" type="nx:nonNegativeUnbounded">
702	<xs:annotation>
703	<xs:documentation>
704	Defines the maximum number of times this element may be used. Its
705	value is confined to zero or greater. Must be greater than or equal to
706	the value for the "minOccurs" attribute.
707	A value of "unbounded" is allowed.
708	</xs:documentation>
709	</xs:annotation>
710	</xs:attribute>
711	<xs:attribute name="stride" use="optional" default="1" type="nx:NX_INT">
712	<xs:annotation>
713	<xs:documentation>
714	The <db:code>stride</db:code> and <db:code>offset</db:code> attributes
715	are used together to index the array of data items in a
716	multi-dimensional array. They may be used as an alternative
717	method to address a data array that is not stored in the standard NeXus
718	method of "C" order.
719
720	The <db:code>stride</db:code> list chooses array locations from the
721	data array with each value in the <db:code>stride</db:code> list
722	determining how many elements to move in each dimension.
723	Setting a value in the <db:code>stride</db:code> array to 1 moves
724	to each element in that dimension of the data array, while
725	setting a value of 2 in a location in the <db:code>stride</db:code>
726	array moves to every other element in that dimension of the
727	data array. A value in the <db:code>stride</db:code> list may be
728	positive to move forward or negative to step backward.
729	A value of zero will not step (and is of no particular use).
730
731	See <db:uri>http://davis.lbl.gov/Manuals/HDF5-1.4.3/Tutor/phypereg.html</db:uri>
732	or <db:emphasis>4. Dataspace Selection Operations</db:emphasis> in
733	<db:uri>http://www.hdfgroup.org/HDF5/doc1.6/Dataspaces.html</db:uri>.
734
735
736	The <db:code>stride</db:code> attribute contains a
737	comma-separated list of integers.
738	(In addition to the required comma delimiter,
739	whitespace is also allowed to improve readability.)
740	The number of items in the list
741	is equal to the rank of the data being stored. The value of each
742	item is the spacing of the data items in that subscript of the array.
743	</xs:documentation>
744	</xs:annotation>
745	</xs:attribute>
746	<xs:attribute name="offset" use="optional" default="1" type="nx:nonNegativeUnbounded">
747	<xs:annotation>
748	<xs:documentation>
749	The <db:code>stride</db:code> and <db:code>offset</db:code> attributes
750	are used together to index the array of data items in a
751	multi-dimensional array. They may be used as an alternative
752	method to address a data array that is not stored in the standard NeXus
753	method of "C" order.
754
755	The <db:code>offset</db:code> attribute
756	determines the starting coordinates of the data array
757	for each dimension.
758
759	See <db:uri>http://davis.lbl.gov/Manuals/HDF5-1.4.3/Tutor/phypereg.html</db:uri>
760	or <db:emphasis>4. Dataspace Selection Operations</db:emphasis> in
761	<db:uri>http://www.hdfgroup.org/HDF5/doc1.6/Dataspaces.html</db:uri>.
762
763	The <db:code>offset</db:code> attribute contains a
764	comma-separated list of integers.
765	(In addition to the required comma delimiter,
766	whitespace is also allowed to improve readability.)
767	The number of items in the list
768	is equal to the rank of the data being stored. The value of each
769	item is the offset in the array of the first data item of that
770	subscript of the array.
771	</xs:documentation>
772	</xs:annotation>
773	</xs:attribute>
774	<xs:attribute name="interpretation" use="optional">
775	<xs:annotation>
776	<xs:documentation>
777	<db:para> This instructs the consumer of the data what the last dimensions
778	of the data are. It allows plotting software to work
779	out the natural way of displaying the data. </db:para>
780
781	<db:para> For example a single-element, energy-resolving, fluorescence detector
782	with 512 bins should have <db:code>interpretation="spectrum"</db:code>. If the
783	detector is scanned over a 512 x 512 spatial grid, the data reported
784	will be of dimensions: 512 x 512 x 512.
785	In this example, the initial plotting representation should default to
786	data of the same dimensions of a 512 x 512 pixel <db:code>image</db:code>
787	detector where the images where taken at 512 different pressure values. </db:para>
788
789	<db:para> In simple terms, the allowed values mean:
790	<db:itemizedlist>
791	<db:listitem><db:para><db:code>scaler</db:code> = 0-D data to be plotted</db:para></db:listitem>
792	<db:listitem><db:para><db:code>spectrum</db:code> = 1-D data to be plotted</db:para></db:listitem>
793	<db:listitem><db:para><db:code>image</db:code> = 2-D data to be plotted</db:para></db:listitem>
794	<db:listitem><db:para><db:code>vertex</db:code> = 3-D data to be plotted</db:para></db:listitem>
795	</db:itemizedlist> </db:para>
796	</xs:documentation>
797	</xs:annotation>
798	<xs:simpleType>
799	<xs:restriction base="xs:string">
800	<xs:enumeration value="scalar"/>
801	<xs:enumeration value="spectrum"/>
802	<xs:enumeration value="image"/>
803	<xs:enumeration value="vertex"/>
804	</xs:restriction>
805	</xs:simpleType>
806	</xs:attribute>
807	</xs:extension>
808	</xs:complexContent>
809	</xs:complexType>
810
811	<xs:complexType name="attributeType">
812	<xs:annotation>
813	<xs:documentation>
814	Any new group or field may expect or require some common attributes.
815	Could contain these elements:
816	<db:itemizedlist>
817	<db:listitem><db:para><db:code>doc</db:code></db:para></db:listitem>
818	<db:listitem><db:para><db:code>enumeration</db:code></db:para></db:listitem>
819	</db:itemizedlist>
820	(This data type is used internally in the NXDL schema
821	to define elements and attributes to be used by users in NXDL specifications.)
822	</xs:documentation>
823	</xs:annotation>
824	<xs:sequence>
825	<xs:element name="doc" type="nx:docType" minOccurs="0">
826	<xs:annotation>
827	<xs:documentation>
828	Description of this <db:code>attribute</db:code>.
829	This documentation will go into the manual.
830	</xs:documentation>
831	</xs:annotation>
832	</xs:element>
833	<xs:element name="enumeration" type="nx:enumerationType"
834	minOccurs="0">
835	<xs:annotation>
836	<xs:documentation>
837	An enumeration specifies the values to be used.
838	</xs:documentation>
839	</xs:annotation>
840	</xs:element>
841	</xs:sequence>
842	<xs:attribute name="name" use="required" type="nx:validItemName">
843	<xs:annotation>
844	<xs:documentation>
845	Unique identifier string (within the enclosing group) for this entity.
846	</xs:documentation>
847	</xs:annotation>
848	</xs:attribute>
849	<xs:attribute name="type" type="nx:primitiveType" default="NX_CHAR">
850	<xs:annotation>
851	<xs:documentation>
852	For <db:code>group</db:code> specifications, the class name.
853	For <db:code>field</db:code> or <db:code>attribute</db:code> specifications,
854	the NXDL data type.
855	</xs:documentation>
856	</xs:annotation>
857	</xs:attribute>
858	</xs:complexType>
859
860	<xs:simpleType name="nonNegativeUnbounded">
861	<xs:annotation>
862	<xs:documentation>
863	A <db:code>nonNegativeUnbounded</db:code> allows values including
864	all positive integers, zero, and the string <db:code>unbounded</db:code>.
865	(This data type is used internally in the NXDL schema
866	to define a data type.)
867	</xs:documentation>
868	</xs:annotation>
869	<xs:union>
870	<xs:simpleType>
871	<xs:restriction base="xs:nonNegativeInteger"/>
872	</xs:simpleType>
873	<xs:simpleType>
874	<xs:restriction base="xs:string">
875	<xs:enumeration value="unbounded" />
876	</xs:restriction>
877	</xs:simpleType>
878	</xs:union>
879	</xs:simpleType>
880
881	<!-- +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
882
883	<xs:complexType name="linkType">
884	<xs:annotation>
885	<xs:documentation>
886	A link to another item. Use a link to avoid
887	needless repetition of information.
888	(This data type is used internally in the NXDL schema
889	to define elements and attributes to be used by users in NXDL specifications.)
890	</xs:documentation>
891	</xs:annotation>
892	<xs:complexContent>
893	<xs:extension base="nx:basicComponent">
894	<xs:attribute name="target" use="required" type="nx:validTargetName">
895	<xs:annotation>
896	<xs:documentation>
897	A link to another item, represented as an
898	absolute path to an existing field such as
899	<db:code>/NXentry/NXinstrument/NXdetector/polar_angle</db:code>.
900	Could contain these elements:
901	<db:itemizedlist>
902	<db:listitem><db:para><db:code>doc</db:code></db:para></db:listitem>
903	</db:itemizedlist>
904	Matching regular expression:
905	<db:programlisting language="c">(/[a-zA-Z_][\w_](:[a-zA-Z_][\w_])?)+</db:programlisting>
906	</xs:documentation>
907	</xs:annotation>
908	</xs:attribute>
909	</xs:extension>
910	</xs:complexContent>
911	</xs:complexType>
912
913	<xs:complexType name="docType" mixed="true">
914	<xs:annotation>
915	<xs:documentation>
916	NXDL allows for documentation on most elements using the <db:code>doc</db:code>
917	element. The documentation is useful in several contexts. The documentation will be
918	rendered in the manual. Documentation, is provided as tooltips
919	by some XML editors when editing NXDL files.
920	Simple documentation can be typed directly in the NXDL: <db:example>
921	<db:title>simple documentation in NXDL</db:title>
922	<db:programlisting language="xml" linenumbering="numbered"
923	><field name="name">
924	<doc>Descriptive name of sample</doc>
925	</field> </db:programlisting>
926	</db:example> This is suitable for basic descriptions that do not need extra formatting
927	such as a bullet-list or a table. For more advanced control, DocBook elements are
928	allowed, such as the <db:code>NXdetector</db:code> specification.
929	Refer to examples in the NeXus base class NXDL files such as <db:code>NXdata</db:code>.
930	Be sure to use the DocBook namespace if the documentation will use any DocBook formatting elements:
931	<db:code>xmlns="http://docbook.org/ns/docbook"</db:code>
932	Could contain these elements:
933	<db:itemizedlist>
934	<db:listitem><db:para><db:emphasis>any</db:emphasis></db:para></db:listitem>
935	</db:itemizedlist>
936	(This data type is used internally in the NXDL schema
937	to define elements and attributes to be used by users in NXDL specifications.)
938	</xs:documentation>
939	</xs:annotation>
940	<xs:sequence>
941	<xs:any minOccurs="0" maxOccurs="unbounded" processContents="lax"/>
942	</xs:sequence>
943	</xs:complexType>
944
945	<xs:complexType name="symbolsType" mixed="true">
946	<xs:annotation>
947	<xs:documentation>
948	Each <db:code>symbol</db:code> has a <db:code>name</db:code> and optional documentation.
949	Please provide documentation that indicates what each symbol represents.
950	For example:
951	<db:programlisting language="xml" linenumbering="numbered"
952	><symbols>
953	<symbol name="nsurf"><doc>number of reflecting surfaces</doc></symbol>
954	<symbol name="nwl"><doc>number of wavelengths</doc></symbol>
955	</symbols></db:programlisting>
956	</xs:documentation>
957	</xs:annotation>
958	<xs:sequence>
959	<xs:element name="doc" type="nx:docType" minOccurs="0" maxOccurs="1">
960	<xs:annotation>
961	<xs:documentation>
962	Describe the purpose of this list of <db:code>symbols</db:code>.
963	This documentation will go into the manual.
964	</xs:documentation>
965	</xs:annotation>
966	</xs:element>
967	<xs:element name="symbol" minOccurs="0" maxOccurs="unbounded">
968	<xs:annotation>
969	<xs:documentation>
970	When multiple <db:code>field</db:code>s share the same dimensions, such as the dimension scales
971	associated with plottable data in an <db:code>NXdata</db:code> group, the length of each
972	dimension written in a NeXus data file should be something that can be tested by the
973	data file validation process.
974	</xs:documentation>
975	</xs:annotation>
976	<xs:complexType>
977	<xs:sequence>
978	<xs:element name="doc" type="nx:docType" minOccurs="0" maxOccurs="1">
979	<xs:annotation>
980	<xs:documentation>
981	Describe the purpose of this <db:code>symbol</db:code>.
982	This documentation will go into the manual.
983	</xs:documentation>
984	</xs:annotation>
985	</xs:element>
986	</xs:sequence>
987	<xs:attribute name="name" type="nx:validItemName">
988	<xs:annotation>
989	<xs:documentation>
990	Mnemonic variable name for this array index symbol.
991	</xs:documentation>
992	</xs:annotation>
993	</xs:attribute>
994	</xs:complexType>
995	</xs:element>
996	</xs:sequence>
997	</xs:complexType>
998
999	<xs:complexType name="enumerationType">
1000	<xs:annotation>
1001	<xs:documentation>
1002	An <db:code>enumeration</db:code> restricts the values allowed for a specification.
1003	Each value is specified using an <db:code>item</db:code> element, such as:
1004	<db:code><item value="Synchrotron X-ray Source" /></db:code>.
1005	Could contain these elements:
1006	<db:itemizedlist>
1007	<db:listitem><db:para><db:code>doc</db:code></db:para></db:listitem>
1008	<db:listitem><db:para><db:code>item</db:code></db:para></db:listitem>
1009	</db:itemizedlist>
1010	(This data type is used internally in the NXDL schema
1011	to define elements and attributes to be used by users in NXDL specifications.)
1012	<db:programlisting language="c"
1013	><field name="mode">
1014	<doc>source operating mode</doc>
1015	<enumeration>
1016	<item value="Single Bunch"><doc>for storage rings</doc></item>
1017	<item value="Multi Bunch"><doc>for storage rings</doc></item>
1018	<!-- other sources could add to this -->
1019	</enumeration>
1020	</field></db:programlisting>
1021	</xs:documentation>
1022	</xs:annotation>
1023	<xs:sequence>
1024	<xs:element name="item" minOccurs="1" maxOccurs="unbounded">
1025	<xs:annotation>
1026	<xs:documentation>
1027	One of the prescribed values. Use the <db:code>value</db:code> attribute.
1028	</xs:documentation>
1029	</xs:annotation>
1030	<xs:complexType>
1031	<xs:annotation>
1032	<xs:documentation>
1033	Defines the value of one selection for an <db:code>enumeration</db:code> list.
1034	Each enumerated item must have a value (it cannot have an empty text node).
1035	</xs:documentation>
1036	</xs:annotation>
1037	<xs:sequence>
1038	<xs:element name="doc" type="nx:docType" minOccurs="0" maxOccurs="1">
1039	<xs:annotation>
1040	<xs:documentation>
1041	Individual <db:code>item</db:code>s can be documented
1042	but this documentation will not be printed in the
1043	<db:emphasis>NeXus Reference Guide</db:emphasis>.
1044	When DocBook markup is used,
1045	be sure to use the provided DocBook namespace prefix
1046	(<db:code>db:</db:code>) for any DocBook elements,
1047	such as this example:
1048	<db:programlisting language="xml"><doc><db:para>this is documentation with DocBook markup</db:para></doc></db:programlisting>
1049	</xs:documentation>
1050	</xs:annotation>
1051	</xs:element>
1052	</xs:sequence>
1053	<xs:attribute name="value" use="required">
1054	<xs:annotation>
1055	<xs:documentation>
1056	The value of <db:code>value</db:code> of an <db:code>enumItem</db:code>
1057	is defined as an attribute rather than a name.
1058	</xs:documentation>
1059	</xs:annotation>
1060	</xs:attribute>
1061	</xs:complexType>
1062	</xs:element>
1063	</xs:sequence>
1064	</xs:complexType>
1065
1066	<xs:complexType name="dimensionsType">
1067	<!--
1068	see TRAC ticket #32: http://trac.nexusformat.org/definitions/ticket/32
1069	-->
1070	<xs:annotation>
1071	<xs:documentation>
1072	dimensions of a data element in a NeXus file
1073	(This data type is used internally in the NXDL schema
1074	to define elements and attributes to be used by users in NXDL specifications.)
1075	</xs:documentation>
1076	</xs:annotation>
1077	<xs:sequence>
1078	<xs:element name="doc" type="nx:docType" minOccurs="0">
1079	<xs:annotation>
1080	<xs:documentation>
1081	Documentation might be necessary to describe how the parts
1082	of the <db:code>dimensions</db:code> element are to be used.
1083	</xs:documentation>
1084	</xs:annotation>
1085	</xs:element>
1086	<xs:element name="dim" minOccurs="0" maxOccurs="unbounded">
1087	<xs:annotation>
1088	<xs:documentation>
1089	Specify the parameters for each index of the <db:code>dimensions</db:code>
1090	element with a <db:code>dim</db:code> element.
1091	The number of <db:code>dim</db:code> entries should be equal to
1092	the <db:code>rank</db:code> of the array.
1093	For example, these terms
1094	describe a 2-D array with lengths (<db:code>nsurf</db:code>, <db:code>nwl</db:code>):
1095	<db:programlisting language="c"
1096	><dimensions rank="2">
1097	<dim index="1" value="nsurf"/>
1098	<dim index="2" value="nwl"/>
1099	</dimensions></db:programlisting>
1100	The <db:code>value</db:code> attribute is used by NXDL and also by
1101	the NeXus data file validation tools to associate and coordinate the
1102	same array length across multiple fields in a group.
1103	</xs:documentation>
1104	</xs:annotation>
1105	<xs:complexType>
1106	<xs:attribute name="index" type="nx:NX_INT" use="required">
1107	<xs:annotation>
1108	<xs:documentation>
1109	Number indicating which axis (subscript) is
1110	being described, ranging from 1 up to
1111	<db:code>rank</db:code> (rank of the
1112	data structure). For example, given an array
1113	<db:code>A[i,j,k]</db:code>,
1114	<db:code>index="1"</db:code> would refer to the
1115	<db:code>i</db:code> axis (subscript).
1116	(<db:code>NXdata</db:code> uses <db:code>index="0"</db:code>
1117	to indicate a situation when the specific index is not
1118	known <db:emphasis>a priori</db:emphasis>.)
1119	</xs:documentation>
1120	</xs:annotation>
1121	</xs:attribute>
1122	<xs:attribute name="value" type="nx:NX_CHAR">
1123	<xs:annotation>
1124	<xs:documentation>
1125	Integer length (number of values), or mnemonic symbol
1126	representing the length of this axis.
1127	</xs:documentation>
1128	</xs:annotation>
1129	</xs:attribute>
1130	<xs:attribute name="ref" type="nx:NX_CHAR">
1131	<xs:annotation>
1132	<xs:documentation>
1133	The dimension specification is the same as
1134	that in the <db:code>ref</db:code> field, specified either by a relative path,
1135	such as <db:code>polar_angle</db:code> or <db:code>../Qvec</db:code> or absolute path, such as
1136	<db:code>/entry/path/to/follow/to/ref/field</db:code>.
1137	</xs:documentation>
1138	</xs:annotation>
1139	</xs:attribute>
1140	<xs:attribute name="refindex" type="nx:NX_CHAR">
1141	<xs:annotation>
1142	<xs:documentation>
1143	The dimension specification is the same as
1144	the <db:code>refindex</db:code> axis within the <db:code>ref</db:code> field.
1145	Requires <db:code>ref</db:code> attribute to be present.
1146	</xs:documentation>
1147	</xs:annotation>
1148	</xs:attribute>
1149	<xs:attribute name="incr" type="nx:NX_CHAR">
1150	<xs:annotation>
1151	<xs:documentation>
1152	The dimension specification is related to
1153	the <db:code>refindex</db:code> axis within the <db:code>ref</db:code> field by an
1154	offset of <db:code>incr</db:code>. Requires <db:code>ref</db:code> and <db:code>refindex</db:code>
1155	attributes to be present.
1156	</xs:documentation>
1157	</xs:annotation>
1158	</xs:attribute>
1159	</xs:complexType>
1160	</xs:element>
1161	</xs:sequence>
1162	<xs:attribute name="rank" type="nx:NX_CHAR">
1163	<xs:annotation>
1164	<xs:documentation>
1165	Rank (number of dimensions) of the data structure.
1166	For example: <db:code>a[5]</db:code> has <db:code>rank="1"</db:code> while
1167	<db:code>b[8,5,6,4]</db:code> has <db:code>rank="4"</db:code>.
1168	See <db:uri>http://en.wikipedia.org/wiki/Rank_(computer_programming)</db:uri>
1169	for more details.
1170	</xs:documentation>
1171	</xs:annotation>
1172	</xs:attribute>
1173	</xs:complexType>
1174
1175	</xs:schema>

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