[r2004-11-08 20:59:46 by vbenzake] Veo add more queries

Original author: vbenzake
Date: 2004-11-08 20:59:46+00:00

web/tutorial/queries.xml

@@ -369,6 +369,71 @@ where t1=t2
 </section>
 
 
+<section title="More complex Queries: on the power of patterns">
+<sample><![CDATA[
+<bib>
+    select <book (a)> x
+      from <book (a)>[ (x::(Any\Editor)|_ )* ] in bib 
+]]>
+</sample>
+
+<p>
+This expression returns all book  in bib but removoing the editor element.
+If one wants to write more explicitly:
+</p>
+<sample><![CDATA[
+    select <book (a)> x
+      from <book (a)>[ (x::(Any\<editor>_)|_ )* ] in bib
+]]>
+</sample>
+<p>Or even:
+</p>
+<sample><![CDATA[
+    select <book (a)> x
+      from <book (a)>[ (x::(<(_\`editor)>_)|_ )* ] in bib
+]]>
+</sample>
+<p>Back to the first one:</p>
+<sample><![CDATA[
+<bib>
+    select <book (a)> x
+      from <(book) (a)>[ (x::(Any\Editor)|_ )* ] in bib
+]]>
+</sample>
+<p>
+This query takes any element in bib, tranforms it in a book element and
+removes sub-elements  editor (but you will get a warning as capture variable book in the from is never used.
+</p>
+<sample><![CDATA[
+    select <(book) (a)> x
+      from <(book) (a)>[ (x::(Any\Editor)|_ )* ] in bib
+]]
+</sample>
+<p> Same thing but without tranforming tag to  "book".
+More interestingly:</p>
+<sample><![CDATA[
+    select <(b) (a\id)> x
+      from <(b) (a)>[ (x::(Any\Editor)|_ )* ] in bib
+]]>
+</sample>
+<p>removes all "id" attribute (if any) from the attributes of the element in bib.
+</p>
+<sample><![CDATA[
+
+    select <(b) (a\id+{bing=a.id})> x
+      from <(b) (a)>[ (x::(Any\Editor)|_ )* ] in bib
+]]>
+</sample>
+<p>Changes attribute id=x into bing=x
+However, one must be shure that each element in bib has an "id" attribute
+if such is not the case the expression is ill-typed. If one wants to perform this only for those elements which certainly have an "id" attribute then:
+</p>
+<sample><![CDATA[
+    select <(b) (a\id+{bing=a.id})> x
+      from <(b) (a&{id=_}))>[ (x::(Any\Editor)|_ )* ] in bib
+]]>
+</sample>
+</section>
 <section title="An unorthodox query: Formatted table generation">
 
 <p>