I can easily support this proposal. The only "downside" of restricting sequences from having lengthKind is that you will have to introduce a named "tier" of an element in your logical DFDL model when you need to model what is really only a physical implementation concept, of a box surrounding data. But I've always been in favor of avoiding the slippery slope where a DFDL schema is supposed to both describe the represenatation as well as exhibiting a logical model that someone likes. To me the DFDL schema is very constrained by what is required by the physical model, and transformations outside of the DFDL schema are going to "tidy up" the model and remove artifacts of representation. The element tier you need in this case to express the length of a "box" surrounding content is such a representation artifact. To me the slippery slope of allowing sequences to be almost like unnamed elements is a slope we very much want to avoid, and as you point out, we're already doing that by eliminating occurs behavior on them for DFDL. Thought: if you are going to need to transform the DFDL-described data anyway, then introducing named tiers for these kinds of complex physical features actually makes such transformation easier to express, because the xpath expressions to address various parts of the DFDL-described data are more obvious. ...mike Mike Beckerle | OGF DFDL WG Co-Chair | CTO | Oco, Inc. Tel: 781-810-2125 | 100 Fifth Ave., 4th Floor, Waltham MA 02451 | <mailto:mbeckerle.dfdl@gmail.com> mbeckerle.dfdl@gmail.com _____ From: dfdl-wg-bounces@ogf.org [mailto:dfdl-wg-bounces@ogf.org] On Behalf Of Steve Hanson Sent: Wednesday, April 29, 2009 6:51 AM To: dfdl-wg@ogf.org Subject: [DFDL-WG] DFDL lengthKind on complex objects I have a long-standing concern about the usability of dfdl:lengthKind, which others in IBM are encountering when modeling real life formats such as EDI. My main concern is below. For example, what's the semantic of setting different values on the element and the sequence? <xs:element name="container" dfdl:lengthKind="implicit"> <xs:complexType> <xs:sequence dfdl:separator="@" dfdl:lengthKind="implicit"> <xs:element name="one" type="xs:string" dfdl:lengthKind="delimited" /> <xs:element name="two" type="xs:string" dfdl:lengthKind="delimited" /> <xs:element name="three" type="xs:string" dfdl:lengthKind="delimited" /> </xs:sequence> </xs:complexType> </xs:element> It gets even more noticeable if I set a scoping dfdl:lengthKind on the complex type. I propose that we limit dfdl:lengthKind to elements only. It means that the length of a xs:sequence or xs:choice is always and implicitly given by its chidren, and if you want to provide an explicit length or a length prefix you must use a complex element to wrap the sequence or choice. We have looked at the implications on dfdl:choiceKind for choices, and dfdl:occursKind on arrays, and the proposal works happily in those scenarios. There's an analogy here with not alowing sequences and choices to repeat, only elements. It also simplifies the grammar, in the sense that any excess fill characters in a 'box' are always considered part of the element when parsing. I'd like to discuss this on today's call. Regards Steve Hanson Programming Model Architect WebSphere Message Brokers Hursley, UK Internet: smh@uk.ibm.com Phone (+44)/(0) 1962-815848 _____ Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU