Database vs XML document archive

I'm trying to understand the differences between a XML document archive
versus a relational data base.

What are their advantages and disadvantages?



- Hallgeir

Hallgeir Stuenes

I've not looked under the hood of an XML document archive, but from my
casual reading and my working indirectly with with them:

* they are not relational databases
* they do not have support for SQL; "querying" capability is probably
limited to what the vendor provides in a proprietary API

I hope someone else will respond to your quest and provide a better
response than mine.

enrique wrote:
> I've not looked under the hood of an XML document archive, but from my
> casual reading and my working indirectly with with them:
>
> * they are not relational databases
> * they do not have support for SQL; "querying" capability is probably
> limited to what the vendor provides in a proprietary API

Leaving aside the confusing issue of what "an archive" actually is,
I think your second point is unlikely: I would expect any current
XML storage system that has a search capability to use one of the
many XML search engines and provide an interface using XQuery. I
can't think of any good reason why "an XML document archive" would
need SQL support.

It is a mistake to expect to be able to use SQL to search information
which may not be meaningfully put into relational form. If you are
dealing exclusively with e-commerce data, where your XML is just a
verbose representation of traditional rectangular data (rows and cols)
then it is possible to map the features of SQL onto a relational
data model. But I contend that if your XML information is traditional
text documents, a relational model is probably not as useful as the
structural access provided in (for example) XSLT by XPath, and the
query access provided by XQuery.

[OP]
> I'm trying to understand the differences between a XML document archive
> versus a relational data base.

An XML document archive is for storing XML documents.
A relational database is for storing relational data.
If your XML documents can be normalised to the relational model, or
if your relational data can be expressed adequately in XML, feel free
to use either system, otherwise pick the right tool for the job.

///Peter
--
XML FAQ: http://xml.silmaril.ie/

enrique wrote:
> * they do not have support for SQL; "querying" capability is probably
> limited to what the vendor provides in a proprietary API

XQuery is intended to occupy this sort of role for data stored as an XML
document or infoset.

Some recent tools may be able to intermix SQL to explore logical
relationships and XQuery to explore structure. I *think* the most recent
release of DB2 can do that, since it's a full relational database with
an XML infoset datatype rather than only supporting one or the other.


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