Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Tue, 28 Jun 2005 15:28:48 +0200

Marty Kraimer wrote:

On Jun 27, 2005, at 10:44 AM, Ralph Lange wrote:

Iirc, at the SLAC meeting we were agreeing on an additional

dataAccess traversal() method that yields the complete property

structure together with the native types of the properties. (NB: And

the access rights info?!).

Those native types have to be well-known, size-fixed types that have

a tag which is defined for the server and client side. So that the

server can show the correct native type if asked for. So that the

client can ask for and understand what's behind a certain property

and use a local type that is wide enough to hold the data.

I sent my last message before I saw this message. Thus you are

supporting an introspection interface. Good.

I don't understand. The main feature of dataAccess *is* an introspection

interface. Always has been. From day one for the last five years. The

traverse() methods have been there for ages.

So: By supporting dataAccess I am supporting an introspection interface.

Of course.

The types that dataAccess uses in its interface to the data, should

by all means be the native types of the language that a certain

implementation of dataAccess is written in.

I would like a client app in any language to be able to find out that

a certain value's native type is "unsigned int32", but I would also

like the same client app to freely choose data types of its language

for its data instead of forcing all client data to be of type

epics... If the interface is to be simple, it must use the simple

types of its language.

For any info that goes over the network I do not agree. I think

architecture independent types are what is needed.

I disagree. And network or not is definitely not the point. DataAccess

doesn't have anything to do with network.

A Java client app must be able to use dataAccess to address stuff in a

C++ library. Locally on the same node, no network involved. Still I want

the Java client to be able to find out the native type of a property is

"unsigned int64" but use Java native types (e.g. a bitfield) in the

dataAccess interface.

For CA, the dataAccess list of well-known primitive types must be

accompanied by a description of how these primitives are sent over the

network. That way CA can be used as a network transport for dataAccess.

But separate things should be kept separately:

Data Access uses native types "outside" (in the API) and defines a list

of well-known size-fixed primitive types "inside".

Channel Access defines a network representation for these primitive

types and provides network transport for dataAcccess property catalogs.

Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System