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1 \documentclass{ivoa}
2 \input tthdefs
3
4 \usepackage{todonotes}
5 \usepackage{listings}
6 \lstloadlanguages{XML,sh,SQL}
7 \lstset{flexiblecolumns=true,tagstyle=\ttfamily, showstringspaces=False}
8
9 \ivoagroup{Edu IG}
10
11 \author{Molinaro, M.}
12 \author{Demleitner, M.}
13 \author{Ramella, M.}
14 \author{Iafrate, G.}
15
16 \editor{Molinaro, M.}
17
18 \SVN$Rev$
19 \SVN$Date$
20 \SVN$URL$
21
22 \previousversion{First published version}
23
24
25 \title{Educational Resources in the Virtual Observatory}
26
27 \begin{document}
28
29 \begin{abstract}
30
31 The goal of this IVOA Note is to introduce and explain practices followed
32 and requirements found while creating and
33 deploying astrophysical resources
34 dedicated to educational purposes ranging from pre-school outreach
35 material to courseware intended for active researchers
36 within the standard VO framework.
37 Issues, proposed solutions and desirables are here reported to be
38 possibly taken into account in future modifications of relevant
39 standards.
40
41
42
43 \end{abstract}
44
45
46 \section{Introduction}
47
48 Advances in technology and communications are creating new and exciting
49 opportunities for teachers to bring astronomy into their
50 classrooms. As the VO makes science-grade data publicly available and
51 classroom sets of (suitably) networked PCs are now standard in schools,
52 exciting projects come within reach of teachers. In order to make things
53 happen, it is important to disseminate material to help teachers
54 tap into these resources. These include documented step-by-step
55 tutorials, use cases explaining how to perform basic astrophysical research
56 using VO tools and resources, and similar exist in various formats and
57 have been translated in different languages.
58
59 At the same time, the VO as used in research is a complex tool,
60 introducing many novel techniques. To enable university level students
61 and active researchers to fully exploit the VO's capabilities, course
62 materials and worked-out use-cases have been found an efficient means of
63 developing the necessary skills far beyond interactive course situations
64 like ``VO Days''. Efficient ways for interested users to locate such
65 material as well as for VO operators to curate it are highly desirable.
66
67 New opportunities also come on the observational side.
68 There is a growing availability of remotely controlled
69 telescopes dedicated to education in many countries world-wide, from the
70 Bradford Robotic Telescope\footnote{\url{http://www.telescope.org}} on Mount
71 Teide, Tenerife
72 to the radio telescopes of the Radio Physics
73 Lab\footnote{\url{http://www.ncra.tifr.res.in/rpl}}, IUCAA, Pune.
74 In some cases, educational telescopes are
75 linked into a network with the aim of guaranteeing the best observing conditions,
76 including deep sky observations during regular daytime school hours, and
77 the best instrument for the particular program of interest. Examples
78 of these networks are
79 iTelescope.net\footnote{\url{http://www.itelescope.net}} and
80 EuHOU-MW\footnote{\url{http://euhou.obspm.fr/public}}.
81
82
83
84 As telescopes enter classrooms more frequently, interest is growing for a
85 public archive of observations and hence for publishing and curation tools,
86 together with the basic applications needed to retrieve, display
87 and analyze data. The VO already includes most of the technology needed
88 to satisfy the requests of educational observatories. In fact, since several
89 years, VO, and in particular the European project EuroVO, is devoting part
90 of its resources to
91 education\footnote{\url{http://wwwas.oats.inaf.it/aidawp5}}. It is
92 therefore a natural decision for VO to tackle the problem of publishing
93 educational data in VO archives.
94
95
96 Resource registration for both educational data services and documents
97 is the most appropriate approach toward making educational resources
98 available within the VO. While
99 technically this may seem trivial, keeping too technical
100 research services out of the the resources devoted to education will
101 require some effort, that will also be needed in order to avoid contaminating
102 VO professional research with obviously inadequate material.
103
104 In the next section we discuss the idea of educational resources curation, then
105 we work out the use cases and needs for
106 registration of tutorials and documents. Finally, we discuss the idea of introducing language
107 internationalization in the resources.
108
109
110
111 \section{A Curated Registry for Education}
112
113 \label{sect:curreg}
114
115
116 From a technical point of view the registration of educational services
117 does not require extensions
118 to the existing for VOResource standard \citep{2008ivoa.spec.0222P}.
119 The only real need for investigating changes to what already exists is due to a
120 use case's distinction between resources to be used in teaching and dissemination
121 versus all the research driven resources that exist in the VO.
122
123
124
125 For simplicity here we will distinguish these two groups of resources as
126 \emph{educational}
127 and
128 \emph{professional}
129 but without any intent of putting them
130 on different levels of importance.
131
132
133
134 \subsection{Educational vs. Professional Resources}
135
136 \label{sect:eduvspro}
137
138
139 On the one side, teachers and educators may find it difficult to filter out
140 from all VO resources those that are suitable for their tutorials and
141 examples. On the other side, educational resources should not be retrieved
142 by a standard professional query.
143 Given that it is not a matter of data quality, but only a distinction upon
144 the resources' scope, nevertheless this duality leads to an issue about the
145 proper way to tag resources for educational usage.
146
147
148
149 In the next subsection we propose a possible tagging solution, based upon
150 the existing
151 \vorent{ContentLevel}
152 element of VOResource, but requiring a small change
153 to it. The subsequent subsection describes the idea of a
154 curated registry for educational resources and the reasons for it to exist.
155
156
157
158 \subsection{ContentLevel granularity issue}
159
160 \label{sect:contentlvl}
161
162 VOResource already has the
163 \vorent{ContentLevel}
164 element
165 allowing data publishers to optionally identify their resources as being
166 suitable for one or more of the following audiences:
167
168
169 \begin{itemize}
170
171 \item General{}
172
173 \item Elementary Education{}
174
175 \item Middle School Education{}
176
177 \item Secondary Education{}
178
179 \item Community College{}
180
181 \item University{}
182
183 \item Research{}
184
185 \item Amateur{}
186
187 \item Informal Education{}
188
189 \end{itemize}
190
191 This element turns out to be misused by many publishers, presumably because
192 it is not really clear what the subtle differences between the available
193 possibilities are; also, to require a fairly substantial enumeration to
194 convey ``for school use'' seems, in retrospect, not likely to promote
195 widespread adoption. We hence propose to simplify the content model
196 to:
197
198
199 \begin{itemize}
200
201 \item General{}
202
203 \item Research{}
204
205 \item Amateur{}
206
207 \end{itemize}
208
209 We expect this to reach two goals:
210
211 \begin{itemize}
212
213 \item to make publishers to better describe (on the average)
214 their resources{}
215
216 \item to providing a tagging solution that suits a first filtering
217 on the resources at client level{}
218
219 \end{itemize}
220
221 Of course, the chance to
222 add an
223 \emph{Educational}
224 value option to this shrinked list, or even
225 substitute it to the
226 \emph{General}
227 one, would be a valuable change.
228
229
230
231 This change in the already existing standard will require only
232 a small effort to update already registered resources because nearly 97\% of
233 them currently have \vorent{ContentLevel} set to
234 \emph{research}, about 2\% of them have
235 no \vorent{ContentLevel} defined at all and only the remaining have a different value
236 (or set of values) set for this element (Appendix \ref{app:clcurrval} details better these
237 figures).
238
239
240 Until the change in VOResource can be performed, it
241 can work as a ``best practice'' recommendation, possibly even at a
242 registry level, where registries can map existing
243 \vorent{ContentLevel} values
244 of
245 \emph{University}
246 to
247 \emph{Research}
248 and
249 everything else except
250 \emph{Amateur}
251 to
252 \emph{General}.
253 .
254
255
256 \subsection{Curating the Edu Registry}
257
258 \label{sect:edureg}
259
260
261 Even in the case of the simplified
262 \vorent{ContentLevel}
263 tagging system
264 a curated registry for educational VO resources will be useful for
265 educators in order to let their students work with a registry without having to
266 worry about confusing material or overwhelming data sizes. A good example
267 for this is the educational version of the Aladin sky atlas that has a
268 built in, curated set of resources suitable for educational level
269 tutorials.
270
271
272
273 Curation will require some effort in managing and keeping up to date
274 such a registry but, most important, it is subjected to some restrictions coming from
275 the IVOA resource registry architecture.
276
277
278
279 If such a registry were a standard publishing registry as laid down in
280 Registry Interfaces
281 \citep{2009ivoa.spec.1104B},
282 its resources would be harvested by the full registries: this means
283 that any dedicated educational resource would end up in the full VO
284 set of resources. For reasons mentioned above, this is not
285 desirable.
286
287
288 If it were to be a full registry, it will harvest itself all the existing
289 resources, and not all of them will fit, or be suitable for, the educational
290 scope the registry has to be preserved for.
291
292
293
294 We need a resource (the curated, in Registry Interfaces
295 parlance, local, registry) capable of:
296
297 \begin{itemize}
298
299 \item
300 \emph{selectively}
301 harvesting the existing VO resources
302 (e.g., from a full registry);{}
303
304 \item register its own educational resources without being directly
305 harvested by full registries (e.g., this could be done using a
306 sibling publishing registry dedicated to host those educational
307 resources that are to be harvested by the standard full registries.{}
308
309 \end{itemize}
310
311 This solution, also presented in Fig. 1, will not touch the existing architecture
312 while giving flexibility for the emerging educational resources to
313 be curated.
314
315
316
317 \begin{figure}
318
319 \includegraphics[width=0.9\textwidth]{curation.png}
320 \caption{Graphic illustration
321 of the connecting interfaces between full registries and the educational
322 curated one. The
323 \emph{auxiliary}
324 publishing is the only automatic token
325 from the edu part.}
326 \label{fig:curation}
327 \end{figure}
328
329 \section{Registering Texts}
330
331 \label{sect:regext}
332
333 Educational material is not only about services – text-like material
334 like tutorials, worked-out use cases, or textbook-like material are at
335 least as important. Within the VO community, there is a large body of
336 educational material for a wide variety of audiences ranging from pre-school to
337 researchers:
338
339 \begin{itemize}
340
341 \item EURO-VO AIDA WP5 -- \url{http://wwwas.oats.inaf.it/aidawp5/eng_download.html}
342
343 \item EURO-VO Scientific Tutorials -- \url{http://www.euro-vo.org/?q=science/scientific-tutorials}
344
345 \item GAVO tutorials --
346 \url{http://www.g-vo.org/pmwiki/Documents/Tutorials}
347
348 \item CDS tutorials -- \url{http://cdsweb.u-strasbg.fr/tutorials/}
349 \end{itemize}
350
351
352 To date, such material has been collected informally by the various
353 projects on plain web pages. It is, in consequence, hard to find, with
354 knowledge of its existence often passed on antecdotically. In order to improve upon
355 this situation, we
356 propose to keep record of educational material in the VO Registry.
357
358 The VO already has a registry extension for standards, which of
359 course are also text-like, StandardsRegExt \citep{2012ivoa.spec.0508H}. This extension,
360 however, focuses on metadata important for standards – e.g.,
361 vocabularies and status – that is not pertinent for educational
362 material. Conversely, it is not concerned with document language (which
363 can safely be assumed to be English for standards), and it disregards
364 the issue of locating formatted and source versions, which for educational
365 material is important.
366
367 Therefore, we believe text-like material should be described in a
368 registry extension of its own: DocRegExt.
369
370
371 \subsection{Use Cases}
372
373 \label{sect:regext-usecases}
374
375 The design of DocRegExt has been guided by the desire to fulfill the
376 following discovery cases:
377
378
379 \begin{itemize}
380
381 \item Is there a tutorial covering discovering intermediate mass black
382 holes? (Standard VOResource is sufficient){}
383
384 \item Is there a tutorial covering working with X-Ray data? (Standard
385 VOResource is sufficient){}
386
387 \item Is there a tutorial dealing with planets suitable for school use?
388 (Standard VOResource is sufficient){}
389
390 \item Is there a tutorial dealing with planets suitable for school use in
391 Italian? (That requires the declaration of the document language){}
392
393 \item What are the subjects of maintained (in the sense of: probably
394 working in the VO as found by the students) tutorials?
395 (The active flag of standard VOResource is
396 unsuitable here since even outdated resources will still be accessible;
397 therefore, we introduce the maintained flag){}
398
399 \item Are there tutorials using redshifts? (This is solved by allowing
400 table metadata in DocRegExt){}
401
402 \item Where can I find an editable version of tutorial ivo://auth/tut1?
403 (This is solved by allowing multiple access URLs with different content
404 types, which should be sufficient to allow answering the question){}
405
406 \item Are there translations of tutorial ivo://auth/tut2? (This is covered
407 by the recommendations on declaring relationships between text-like
408 resources){}
409
410 \item Is there material using service ivo://auth/svc1? (Again, declaring
411 relationships covers this use case){}
412
413 \item Is there material about something visible tonight? (In principle,
414 allowing the coverage element withing DocRegExt resources enables this
415 use case, although as of this writing, the Registry infrastructure does
416 not support spatial discovery).
417
418 \item I found this VO tutorial somewhere on the net (``on a mirror''). Is it
419 the latest version? If not, where can I find an update? (Unless the
420 title of the text changed, standard VOResource should suffice){}
421
422 \end{itemize}
423
424 An important additional use case is enabling an attractive, browsable
425 list of registred educational material. A first attempt at such a
426 service is GAVO's VO Text Treasures (VOTT)
427 service\footnote{\url{http://dc.g-vo.org/VOTT}}. It was found that one
428 requirement resulting from this use case is direct access to formatted
429 material in order to enable thumbnail generation.
430
431 On the use cases of locating editable forms of such texts – which
432 has been found to be necessary fairly regularly – we note in passing
433 that representing source-product relationships is in principle in the
434 domain of provenance and thus not in the Registry's main scope. However, in
435 the case discussed here the relation is so simple and its representation
436 so useful that we propose to include it in a DocRegExt.
437
438 \subsection{A Document Registry Extension}
439
440 %% NOTE: When you change the schema, make Markus run a
441 %% make install-schema
442 %% to update the current "canonical" schema location.
443
444 \label{sect:regext-ext}
445
446 To satisfy the requirements derived above, we have designed a registry extension with
447 two definitions.
448 To avoid unnecessary incompatibilities when migrating to a proper IVOA
449 standard, we use the namespace URI
450
451 $$\hbox{\nolinkurl{http://www.ivoa.net/xml/DocRegExt-1.xsd}}$$
452
453 for DocRegExt even while the schema cannot actually retrieved from
454 there. The canonical schema location until the extension is endorsed by
455 the IVOA is \url{http://docs.g-vo.org/xml/DocRegExt-1.xsd}.
456
457 The recommended schema prefix for DocRegExt is \texttt{doc}.
458
459 To let authors define comprehensive metadata, the schema
460 re-uses the \vorent{vs:CatalogService} type
461 from VODataService 1.1 \citep{2010ivoa.spec.1202P} to construct
462 the \vorent{doc:Document} resource type.
463
464 While the schema does not limit what kinds of capabilities a
465 \vorent{doc:Document} record has -- it is conceivable that tailored
466 services are communicated in this way --, access to actual files is
467 enabled using \vorent{doc:Edition}-typed capabilities. It may be
468 argued that this use of VOResource capabilities stretches their
469 semantics a bit. We argue, however, that these documents can well be
470 understood as parameterless service endpoints. Using capabilities
471 furthermore allows a complete representation of the metadata in RegTAP
472 without any extra tables (cf.~sect.~\ref{sect:docregext-regtap}).
473
474 The resource-level reference URL in \vorent{doc:Document} records should
475 be some sort of landing page with an abstract of the text and links to
476 the full texts and perhaps the document source(s). When using the
477 versioned repository (sect.~\ref{sect:svn-repo}), this could be the
478 top-level README file within the VCS. For simple documents, it is
479 acceptable to use the English-language document itself as
480 \vorent{referenceURL}; documents only available in non-English should
481 provide a landing page with an English-language abstract, though.
482
483 The \vorent{facility} and \vorent{instrument} items should only be set
484 if the text in question actually exploits particular properties of the
485 concrete instrument. A \vorent{tableset} can be given for the central
486 table-like structures a text deals with and facilitates discovery by
487 physics via the UCDs given in the tableset.
488
489 Document-typed resource records should define relations to other
490 general resources (e.g., applications, services,\dots)
491 they use. VOResource 1.1 provides a vocabulary of possible
492 relationships. Document records should preferably use \emph{Cites} and
493 in particular declare relationships to tools. If these are not
494 registred, use the name of their binary name as the name of the related
495 resource; this will very typically be lowercase-only.
496
497 Each \vorent{Edition}-typed capability should
498 correspond to a translation of the document. It
499 is recommended to list the English-language version first if it exists.
500
501 The following description of the \vorent{doc:Edition} capability
502 is generated from the schema file.
503
504 % GENERATED: !schemadoc DocRegExt-1.xsd Edition
505 \begin{generated}
506 \begingroup
507 \renewcommand*\descriptionlabel[1]{%
508 \hbox to 5.5em{\emph{#1}\hfil}}\vspace{2ex}\noindent\textbf{\xmlel{doc:Edition} Type Schema Documentation}
509
510 \noindent{\small
511 An “edition” (typically: translation) of the document.
512 \par}
513
514 \noindent{\small
515 Although for a while, multiple editions of the document in one language
516 may be given (corresponding perhaps to two “major” versions), in
517 general, only the latest version of the document per language should be
518 given.
519
520 At least one vr:WebBrowser-typed interface with
521 role="rendered" must be present. The access URL of the interface
522 points to a rendered version of the edition (preferably in PDF,
523 but HTML is acceptable, too).
524
525 Editors are strongly encourated to also provide an
526 interface with role="source", the accessURL of which should point
527 to an editable version of the document, a version controlled
528 repository, or the like.
529 \par}
530
531 \vspace{1ex}\noindent\textbf{\xmlel{doc:Edition} Type Schema Definition}
532
533 \begin{lstlisting}[language=XML,basicstyle=\footnotesize]
534 <xs:complexType name="Edition" >
535 <xs:complexContent >
536 <xs:extension base="vr:Capability" >
537 <xs:sequence >
538 <xs:element name="language" type="xs:token" minOccurs="1"
539 maxOccurs="1" />
540 <xs:element name="locTitle" type="xs:token" minOccurs="0"
541 maxOccurs="1" />
542 </xs:sequence>
543 </xs:extension>
544 </xs:complexContent>
545 </xs:complexType>
546 \end{lstlisting}
547
548 \vspace{0.5ex}\noindent\textbf{\xmlel{doc:Edition} Extension Metadata Elements}
549
550 \begingroup\small\begin{bigdescription}\item[Element \xmlel{language}]
551 \begin{description}
552 \item[Type] string: \xmlel{xs:token}
553 \item[Meaning]
554 The language this document is (mainly) written in,
555 as an RFC 3066 language code.
556
557 \item[Occurrence] required
558 \item[Comment]
559 The country codes must be given in all lowercase. This
560 results in strings like en-us, de-de, or es-mx.
561
562 This language is also the language for locTitle,
563 irrespective or that element's xml:lang setting.
564
565
566 \end{description}
567 \item[Element \xmlel{locTitle}]
568 \begin{description}
569 \item[Type] string: \xmlel{xs:token}
570 \item[Meaning]
571 \item[Occurrence] optional
572
573 \end{description}
574
575
576 \end{bigdescription}\endgroup
577
578 \endgroup
579 \end{generated}
580
581 % /GENERATED
582
583 \subsection{DocRegExt in RegTAP}
584 \label{sect:docregext-regtap}
585
586 In the relational registry \citep{2014ivoa.spec.1208D}, DocRegExt is
587 straightforwardly represented in the standard VOResource tables. in
588 particular, to find all titles and access urls for documents, one would
589 write:
590
591 \begin{lstlisting}[language=SQL]
592 SELECT res_title, access_url FROM
593 rr.resource
594 NATURAL JOIN rr.interface
595 WHERE
596 res_type='doc:document'
597 and intf_role='rendered'
598 \end{lstlisting}
599
600 The \vorent{language} and \vorent{locTitle} elements from the
601 \vorent{doc:Edition} capability extension are mapped into
602 \verb|res_details| with the following \verb|detail_xpath|s:
603
604 \begin{itemize}
605
606 \item \texttt{/capability/language} -- the document language as an RFC
607 3066 language code.
608 \item \texttt{/capability/locTitle} -- the title in the national
609 languate.
610 \end{itemize}
611
612 The downside of not defining an extra table for the documents is that
613 the query patterns in RegTAP are somewhat clumsy. For instance, to list
614 the English and Italian titles of all texts available in Italian, one
615 has to carefully join two subqueries to \verb|res_details|:
616
617 \begin{lstlisting}[language=SQL]
618 SELECT res_title, loctitle FROM
619 rr.resource
620 NATURAL JOIN (
621 SELECT ivoid, loctitle FROM (
622 SELECT ivoid, cap_index, detail_value as loctitle
623 FROM rr.res_detail
624 WHERE detail_xpath='/capability/locTitle') AS titles
625 NATURAL JOIN (
626 SELECT ivoid, cap_index
627 FROM rr.res_detail
628 WHERE
629 detail_xpath='/capability/language'
630 AND detail_value LIKE 'it_%') AS italiancaps
631 ) as loctitles
632 WHERE
633 res_type='doc:document'
634 \end{lstlisting}
635
636
637 Here is a (slightly abridged) example record\todo{Update this to the new
638 schema}:
639
640 \lstinputlisting[language=XML,basicstyle=\footnotesize]{m1distance-example.xml}
641
642 \subsection{A versioned repository for tutorials}
643
644 \label{sect:svn-repo}
645
646 Registering text document as VO resources allows searching for tutorials
647 and similar
648 material through standard registry interfaces, but keeping
649 tutorials up to date, in their master form and also in their translated
650 versions, is an obviously important management issue not really
651 addressed by the Registry.
652
653 For tracking changes and versions, the standard tool is a version
654 control system. Therefore,
655 a versioned repository (using subversion as the version control system)
656 has been set up at GAVO data
657 center\footnote{\url{http://svn.ari.uni-heidelberg.de/svn/edu/}}.
658 It collects part of the
659 already existing VO tutorials with the goal of preserving them and
660 letting users
661 update and translate them.
662
663 The repository has an internal structure designed to enable:
664
665 \begin{itemize}
666
667 \item different national languages (master language set to english){}
668
669 \item translation vs. master language updates{}
670
671 \item licensing, in order to clarify how and whether a tutorial can be changed or re-used{}
672
673 \item additional materials used by tutorials{}
674
675 \item access roles to allow everyone to access tutorials but prevent untrusted updates or additions to it{}
676
677 \end{itemize}
678
679 Details of this structure are discussed in a \texttt{README} file at the
680 root of the
681 repository\footnote{\url{http://svn.ari.uni-heidelberg.de/svn/edu/README}}.
682 The repository is intended to work as a space for cooperative
683 VO tutorials development.
684
685
686
687
688 \appendix
689
690 \section{ContentLevel values summary}
691
692 \label{app:clcurrval}
693
694
695 This appendix reports some statistics on the usage of the ContentLevel
696 element in \citep{2008ivoa.spec.0222P} as of 2014-01-30, taken from the
697 GAVO RegTAP endpoint http://dc.g-vo.org/tap .
698 There are 14392 useful resources (excluding authorities, standards and
699 similar) that expose 26 different values as their ContentLevel.
700 In table \ref{tab:cldist} these values are reported in order of count.
701
702
703
704 \begin{table}
705 \begin{tabular}{lp{12cm}}
706 \sptablerule
707 \textbf{count}&
708 \textbf{content\_level string}\\
709 \sptablerule
710 13937&research\\
711 290&\\
712 41&university research\\
713 40&general university research amateur\\
714 24&university\\
715 14&university research amateur\\
716 7&general\\
717 5&research general\\
718 4&general research\\
719 3&secondary education community college university research amateur\\
720 3&research university community college\\
721 3&elementary education middle school education secondary education\\
722 3&general university research\\
723 2&research university\\
724 2&research amateur university community college\\
725 2&general informal education\\
726 2&general elementary education middle school education secondary education community college university research amateur informal education\\
727 1&university community college research\\
728 1&general university research amateur informal education\\
729 1&elementary education middle school education secondary education community college university research\\
730 1&general secondary education university research\\
731 1&university research general informal education\\
732 1&research university amateur\\
733 1&elementary education middle school education secondary education community college university research amateur\\
734 1&elementary education middle school education secondary education community college university research amateur informal education\\
735 1&university research amateur informal education\\
736 1&general university research informal education\\
737 \end{tabular}
738 \caption{Empirical distribution of \vorent{ContentLevel}s declared by VO
739 resources.}
740 \label{tab:cldist}
741 \end{table}
742
743
744
745 This table can be easily updated from the same endpoint (or an analogue
746 one) using the following ADQL query:
747
748 \begin{verbatim}
749 SELECT
750 count(*) as cnt, content_level
751 FROM
752 rr.resource
753 WHERE
754 res_type not in ('vstd:servicestandard', 'vg:authority',
755 'vstd:standard', 'va:application', 'vr:organization')
756 GROUP BY content_level
757 ORDER BY cnt DESC
758 \end{verbatim}
759
760 The table shows that only about 1\% of the ContentLevel values use
761 something different and more complex than
762 \emph{research}, when
763 the element is not empty. Morever, of this 1\% (165 resources),
764 61 include the \emph{general} value (roughly 37\% of them),
765 29 (17\%) state that are devoted to some
766 \emph{education} level only,
767 while 148 (90\%) state that are also devoted to some
768 \emph{education} level (up to
769 \emph{university}).
770
771 \bibliography{ivoatex/ivoabib,ivoatex/docrepo}
772
773 \end{document}

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