Author:	Archimedes
Title:	Archimedis Opera non nvlla a Federico Commandino Vrbinate nvper in Latinvm conversa, et commentariis illustrata : quorum nomina in sequenti leguntur [Incl.:] Commentarii in Opera non nvlla Archimedis / Fredericus Commandinus (1578); Regiomontanam Franci Fvndamenta operationvm qvae siunt per tabulam generalem ...(Neuburgi ad Danubium, 1557); Theodosii Sphaericorvm elementorvm libri. III : Ex traditione Maurolyci Messanensis Mathematici ; Menelai sphaericorvm lib. III, ex traditione eiusdem ; Maurolyci sphaericorvm lib. II ; Autolyci de sphaera, quae movetur Liber ; Theodosii de habitationibvs ; Euclidis phaenomena, brevissime demonstrata ; Demonstratio et praxis trium tabellarum scilicet sinus recti, foœcundæ, & beneficae ad sphæralia triangula pertinentium ; Compendivm mathematice, mira brevitate exclarißimis Authoribus ; Maurolyci de Sphaera sermo / Theodosius <Bithynius> (Messanae : Spira, 1558)
Year:	1558
Language:	la
City:	Venetiis
Number of pages:	[3], 55, [2], 63, [ca. 35], 72 Bl., 3 Falttaf. : graph. Darst.
Publisher:	Manutius

XQuery:

XQueries are executed against its context (a path relative to the context). The context is the document from which the XQuery is executed. XQueries are namespace aware.

Example 1: return all echo:metadata entries of current document
let $result := //echo:metadata/*
return $result

Example 2: count words of first 3 sentences of current document: let $s := //echo:s
let $first3s := $s[position() < 4]
let $first3Str := string-join($first3s, ' ')
let $wordCounter := count(tokenize($first3Str, '\W+')[. != ''])
return $wordCounter
If you want to query over many documents you could do this for example by specifying the document collection and using an XPath expression relative from this collection

Example 3: (XQuery over all documents): return all authors of all archimedes documents ordered let $coll := collection('/db/mpdl/documents/standard/archimedes')
let $result := $coll/archimedes/info/author
let $orderedResult :=
for $elem in $result
order by $elem
return $elem
return $orderedResult

References: XQuery Language 1.0, see here, Wikipedia article, eXist functions, see here

Xpath
XPath queries are executed against its context (a path relative to the context). The context is the document from which the XPath query is executed.

Example: /archimedes/info/author finds only the author of the document from which the query is executed (and not of all documents). XPath queries are namespace aware.

References: XPath Language 2.0, see: here.