Re: About Saxon XQuery Processor

You may be using the open-source Saxon-HE implementation, which does not =
have a join optimizer; joins are a great deal faster in the commercial =
Saxon-EE implementation.

However, all SQL implementations that I know of run on persistent data =
in a database, and joins usually perform best when you have pre-built =
indexes on the relevant data fields. There are many XQuery =
implementations designed to run on a database environment with a similar =
approach to indexing, and I would expect them to perform equally well. =
In this respect Saxon is different because it works on ad-hoc XML data =
files, with no opportunity to build indexes manually in advance. =
Although Saxon-EE uses indexes to optimize joins, it has to make the =
indexing decisions itself based on the actual query.

Also, I think the equi-join operation is a lot less important when =
dealing with hierarchic data (XML) than when dealing with relational =
data (SQL). Most of the time with XQuery, the relationships you need to =
use in a query are the hierarchic relationships implicit in the XML, =
rather than value-based relationships between primary keys and foreign =
keys. The focus in an optimizer is always on optimizing the constructs =
that are most used.

Michael Kay
Saxonica


> On 18 May 2015, at 18:48, Yoonmoe Lay <[email protected]> wrote:
>=20
> Dear everyone,
>=20
>             I am a computer science master student from
> Myanmar. Now, I am doing analysis of querying system for SQL and
> XQuery. May I know why XQuery ( that used Saxon) is slower than SQL in
> Join queries? I want also to know why XQuery is faster than SQL expect
> Join queries. Please answer my questions as soon as possible. Thank a
> lot.
>=20
> Best Regards,
> Ms. Lwin Moe Aung
>=20
>=20
>=20
>=20