I prefer the hexBinary approach. The disadvantage Mike observes with the array of bytes approach is not limited to conversion to XML. It would also apply to any in-memory tree (SDO etc) built by the DFDL parser. And the element unnecessarily becomes eligible to take the dfdl:occurs annotation. Regards, Steve Steve Hanson WebSphere Business Integration Brokers, IBM Hursley, England Internet: smh@uk.ibm.com Phone (+44)/(0) 1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 07/09/2005 11:23 ----- Mike Beckerle <beckerle@us.ibm. com> To Sent by: Mike Beckerle <beckerle@us.ibm.com> owner-dfdl-wg@ggf cc .org dfdl-wg@gridforum.org, "Robert E. McGrath" <mcgrath@ncsa.uiuc.edu>, owner-dfdl-wg@ggf.org 06/09/2005 21:21 Subject [dfdl-wg] Opaque/BLOB/Uninterpreted/Raw - also hexBinary - (was Re: split into multiple topics - Re: [dfdl-wg] Issues: additional data types) re: Opaque or uninterpreted or raw fields. These are sometimes called Blobs, though database people reserve that term for the acronym "BLOB" which stands for Binary Large Object, which has to do with size being too large for the smaller binary SQL type objects. I.e., there's no such thing as a small BLOB in databases. I think in our mailing list we've used blob to mean "opaque bytes" of any size at all. I believe use of the 'hexBinary' type is also probably this same topic. I.e., how to deal with data where you don't know its proper interpretation, though you can express how big it is so that we can at least copy it from place to place. I think there are two choices here. One is just use "occuring" bytes. E.g., here's uniterpreted data of length 1234 bytes: <element name="ignoreMe" type="byte" minOccurs="1234" maxOccurs="1234" dfdl:repType="binary"/> This is a basic binary byte array. I think this works fine as a blob/opaque type. I believe we do not need any other kind of raw/opaque type. If we had one, we'd have to have a way to express its length, and be specific about the units of that length, and the above accomplishes that with pretty much minimum baggage. You name it what you want, i.e, "unused" or "dummy" or "ignore" or whatever you want. We might want an annotation to indicate that this data should not be accessed, to distinguish this case from an actually array of bytes that you DO want to access, but I'm not sure that's worth it. Note that the OMG CAM model does have an access control attribute. Perhaps we can use that. However, I doubt it allows distinguishing copy from access. The alternative is to use the "hexBinary" type for this. In that case we need to express the size in the DFDL annotation: <element name="ignoreMe" type="hexBinary" dfdl:repLength="1234" dfdl:repType="binary"/> I can think of one advantage of hexBinary over the occuring bytes approach, which is suppose you do want to use DFDL in the obvious way to convert data into XML format. Never mind that DFDL is supposed to enable avoiding this, suppose it's what you want to do. Then my above byte array for the "ignoreMe" element ends up as: <ignoreMe>0</ignoreMe><ignoreMe>0</ignoreMe><ignoreMe>0</ignoreMe><ignoreMe>0</ignoreMe><ignoreMe>0</ignoreMe><ignoreMe>0</ignoreMe>....<ignoreMe>0</ignoreMe> Which is big compared to: <ignoreMe>000000000000...00</ignoreMe> which is what we'd get if we allow hexBinary as a type. Note that if we add the hexBinary type, you'll still be able to do it the other way, so the hexBinary notion is not strictly speaking necessary or minimalist. ...mikeb Mike Beckerle Architect, Scalable Computing IBM Software Group Information Integration Solutions Westborough, MA Mike Beckerle/Worcester/IBM@IBMUS Sent by: To owner-dfdl-wg@ggf.org "Robert E. McGrath" <mcgrath@ncsa.uiuc.edu> cc 09/02/2005 04:34 PM dfdl-wg@gridforum.org, owner-dfdl-wg@ggf.org Subject split into multiple topics - Re: [dfdl-wg] Issues: additional data types I'd like to split this topic into several distinct ones: Arrays - I have a placeholder for this in the doc. Opaque and "code" types are separate. This is related also to the concept of "open content". Enums Bitfields Pointers Mike Beckerle Architect, Scalable Computing IBM Software Group Information Integration Solutions Westborough, MA "Robert E. McGrath" <mcgrath@ncsa.uiuc.edu> Sent by: owner-dfdl-wg@ggf.org To dfdl-wg@gridforum.org 09/02/2005 03:13 PM cc Subject [dfdl-wg] Issues: additional data types Greetings, Here is an "issue" for the DFDL: additional data types that should be considered. Please see attached. --- Robert E. McGrath National Center for Supercomputing Applications University of Illinois, Urbana-Champaign Champaign, Illinois 61820 (217)-333-6549 mcgrath@ncsa.uiuc.edu (See attached file: DT.htm)