Q/R Relational Queries
Bill
Relational queries?
How commonplace is it for Q/R SCUs to support the extended behavior of
Relational queries?
Thank you.
bill
eric.g...@gmail.com
the processing of C-Find queries invoked under negotiated hierarchical
query SOP Class associations - e.g. allowing Series Modality
(0008,0060) to be used as a match key when querying at the Study Level.
It is fairly rare for Q/R SCPs to support extended negotiation for
relational queries and formally acknowledging they are using relational
logic (and therefore acknowledging their application behavior is not in
compliance with the hierarchical query model requirements).
It is even rarer for Q/R SCUs to support relational query extended
negotiation, which makes the lack of support in SCPs somewhat
understandable.
Basically it comes down to the old aphorism about marriage: "Why buy
the cow when you're getting the milk for free?". Since many SCPs
already provide relational logic in what are supposed to be only
hierarchical queries (and SCUs use it), there is little motivation for
either one to implement additional negotiation logic to "enable"
relational queries. Conversely, there also aren't any DICOM police to
penalize the applications providing relational logic under what is
supposed to be limited to hierarchical query. Even if there were a
DICOM police, it is likely the citizentry wouldn't be happy if the
applications were suddenly forced to start conforming to the
hierarchical query limitations and breaking some very commonly used
query patterns (i.e. queries for study by modality and study level
proxy for body part); but if there were such enforcement, it would be a
motivator for application vendors to start using the relational model
as the DICOM gods intended.
In my experience, I've never seen relational query models negotiated
and used. In discussing the topic, an engineer from IDX told me their
system supports relational query negotiation.
Bill
supporting the extended negotiation?
If yes, this will allow the SCU to have attributes from any query level
in the C-Find-Rq dataset. This basically ignores the restriction put
on by the hierarchical query model. For the real world implementation,
is this correct?
Is it commonplace for SCUs to expect relational behavior from the SCP?
thank you
bill
eric.g...@gmail.com
without first negotiating it; however, I have made the observation that
many vendors do in fact provide some level of relational behavior in
their SCPs. Many did so based on on the need to provide functionality
that the original writers of the standard probably didn't realize they
were disabling with strict compliance to the standard.
Yes - relational query allows attributes from all level/all entities in
the query model to be specified as match keys in the query.
I think the expectations of SCUs (or applications which have an
underlying SCU are all over the place). Traditionally there has been a
pretty transparent flow through from the query parameters specified by
a user in a GUI to the DICOM query interface/results. So - the
"expectations" of the SCU have been the expectations of the end user,
rather than contraints of an automated program. Automated prefetch
algorithms have traditionally used a direct database query that allowed
them to perform relational logic without worrying about hierarchical
contraints the DICOM interface was supposed to be imposing.
There is greater interest now in intra-PACS querying in a discovery
mode and I believe there may be some PACS to PACS interfaces which do
utilize or depend on violations of the hierarchical query contraints.
There was some dicussion on the topic in this news group a year or two
back. You might search back through the archive to locate that
discussion for further information and contacts.
Bill
questions.
bill