RE: Some newbie xml questions
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <Alan.Davey@xxxxxxxxxxxxxxxxx>
- Date: Mon, 11 Oct 2004 22:09:01 +0200
Hi Alan
>So far so good. But no matter what I try, I can't seem to figure out
>how to extract ItemNumber, "Part Id", Quantity, or UnitPrice. Do the
>extract and path strings not work properly for elements without proper
>tags around them?? =20
"elements without proper tags around" are called "attributes".=20
To access them you should add a "@", e.g.:
select extract(value(d),'/LineItem/Part/@Id').getstringval()
from test_po p, =
table(xmlsequence(extract(p.po_xml,'/PurchaseOrder/LineItems/LineItem')))=
d
where p.po_id =3D 1
>Does the validation methods work when validating an xml file against a
>schema definition (xsd) file?
Never had problem with it.
>Its possible that the xsd file in the Oracle docs has errors, so I will
>have to look at it in more detail.
Mhmm... I always develop my XML schemas with XML Spy... therefore they =
are always valid...
I suggest you to carefully check your XML schema before the =
registration.
>What are some of the performance issues that you have seen in regards =
to
>XML files? For an upcoming project, I will be dealing with xml files
>~17MB in size for an upcoming project. =20
If you want to speed-up selects you should store the XML as =
object-relational. In this case you should carefully choose the physical =
implementation of the collections (varray or nested tables?).
If you want to speed-up loads you should store the XML as LOB.
>How do I index the po_xml column
>to better handle information retrieval? Do I create function based
>indexes using the extract() methods for those paths that I will be =
going
>after?
Yes. Another possibility, if you use object-relational, is to directly =
create the indexes on the object tables. Notice that the CBO is able to =
perform query rewrites on them, i.e. if you have a select with the =
extract() function it is able to use an index created on the underlying =
object tables. The opposite is true as well.
Good luck
Chris
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