To me, no properties apply to a complex type, rather they apply to the model
group (sequence or choice) which is the meaning of the complex type.
That is, we don't have to distinguish a complex type from the model group
that defines it.
...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: Alan Powell [mailto:alan_powell@uk.ibm.com]
Sent: Tuesday, May 19, 2009 11:50 AM
To: mbeckerle.dfdl@gmail.com
Cc: dfdl-wg@ogf.org; dfdl-wg-bounces@ogf.org
Subject: Re: [DFDL-WG] Grammar issue - simple and complex asymetry
Mike
That looks reasonable.
However as you must still be able to specify dfdl:initiator/terminator on
the complexType for scoping we need to somehow make it clear that the
grammar describes where the properties APPLY not where they are SPECIFIED.
Do any properties APPLY to a complexType?
Alan Powell
MP 211, IBM UK Labs, Hursley, Winchester, SO21 2JN, England
Notes Id: Alan Powell/UK/IBM email: alan_powell@uk.ibm.com
Tel: +44 (0)1962 815073 Fax: +44 (0)1962 816898
From: "Mike Beckerle"
To:
Date: 13/05/2009 20:09
Subject: [DFDL-WG] Grammar issue - simple and complex asymetry
_____
The draft 034 grammar productions do not allow for a separate prefix/suffix
for a simple type as distinguished from the element having that type.
Draft 034 does allow for an element of complex type to have a separate
prefix and suffix for the element itself and another one for the sequence or
choice inside it.
I've come to believe this is a mistake and I suggest a fix below.
Right now the grammar is:
Element = SimpleElement | ComplexElement
SimpleElement = Prefix SimpleContent Suffix
SimpleContent = StringText // terminal. No more prefixes/suffixes
ComplexElement = Prefix ComplexContent Suffix
ComplexContent = Sequence | Choice
Sequence = Prefix SequenceContent Suffix
Choice = Prefix ChoiceContent Suffix
So, if I do:
<complexType dfdl:initiator="[" dfdl:terminator="]">
...
<element name="y">
<complexType>
<sequence dfdl:separator="," >
<element name="x" type="int"/>
<element name="z" type="int"/>
</sequence>
</complexType>
</element>
...
</complexType>
I have two prefix opportunities. I can flatten the productions above to:
ComplexElement = Prefix Prefix SequenceContent Suffix Suffix
An instance of this type would look like [[[5],[6]]]. That is, for complex
types, there are separate prefix and suffix regions for the element, and for
the model-group which makes up its content.
The first [ initiates element y.
The second [ initiates the sequence
The third [ initiates element x.
This same behavior is not true for simple types:
<complexType dfdl:initiator="[" dfdl:terminator="]">
...
<element name="y" >
<simpleType>
<restriction base="int"/>
</simpleType>
</element>
...
</complexType>
This can only mean [5]. The grammar, as formulated in draft 034, does not
allow for more than one prefix or suffix.
The [ is the initiator of element y.
I believe we should fix this as follows. New grammar:
Element = SimpleElement | ComplexElement
SimpleElement = Prefix SimpleContent Suffix
SimpleContent = StringText
ComplexElement = ComplexContent // Note: no more surrounding prefix suffix.
ComplexContent = Sequence | Choice
Sequence = Prefix SequenceContent Suffix
Choice = Prefix ChoiceContent Suffix
The above grammar arranges for an element of complex type and its model
group to both taken together specify a single prefix and suffix.
Revisiting our example (just repeating it here):
<complexType dfdl:initiator="[" dfdl:terminator="]">
...
<element name="y">
<complexType>
<sequence dfdl:separator="," >
<element name="x" type="int"/>
<element name="z" type="int"/>
</sequence>
</complexType>
</element>
...
</complexType>
An instance now would look like [[5],[6]]
The first [ is the initiator of element y, which is the same as the
initiator of the sequence that is its type.
The second [ is the initiator of element x. (which is the same as the
initiator of the int that is its type)
I believe this is more sensible, as it makes the behavior of simple and
complex types more similar.
It begs the question of how one combines conflicting properties on an
element with the properties on the type, and even the model group inside the
type in the complex case. Because all these properties are describing the
same syntax fields in the grammar.
That's a separate topic in a subsequent email.
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