Re: Antw: Re: revised gda-xml-query.dtd

["Gerhard Dieringer" <DieringG eba-haus de>]

Hi Vivien,

you wrote:

> ...
> This means that the <array> element cannot be defined in the DTD (as for
> other nonstandard data types), which is not really nice!
> 
> There is a difference between arrays and other data types like
> varchar: arrays need one arg to tell them the data type stored and others for
> the dimensions, and are written type[?][?][?]... Other data types like varchar
> need one arg for its size and is written varchar(?). We could imagine other
> data types which would require more args and would be written dummy(?,?).
> 
> I propose the creation of several new elements:
> <!ELEMENT datatypearg (datatypedef)?>
> <!ATTLIST datatypearg
>           order (1|2|3|4|5|6|7|8|9|10) #REQUIRED
>           value NMTOKEN #IMPLIED>
> 
> <!ELEMENT datatypedef (datatypearg)*>
> <!ATTLIST datatypedef
>            name NMTOKEN #IMPLIED>
> 
> <!ELEMENT fielddef (datatypedef)?>
> <!ATTLIST fielddef
>           id   ID      #IMPLIED
>           name NMTOKEN #REQUIRED
>           type NMTOKEN #REQUIRED
>            size CDATA   #IMPLIED
>            notnull (yes|no) "no">
> ....

I'm sorry, but I think this solution has also a drawback. If I understood you right, you criticized by proposal because it's not definded in the DTD and therefore can't be validated. But your solution only allows some kind of pseudo-validation, because you have rules, that nowhere occur in the DTD
(because of the limited posibilities of a DTD):

> * if the type name is "array", then the first datatypearg element given MUST be
> the data type for the array, and the next ones the dimensions of the array.

DTDs don't care about the values of attributes and therefore a query may be valid with regard to the DTD but invalid with regard to XML-query.

BTW the same problem occures in other elements as for example  your 'query' or my 'trailer'. In all these cases the valid (with regard to XML-query) structure
depends an attribute values that can't be valided (with regard to the XML-DTD).

I see two ways, actually only one ;-) , to go on

1.) we ignore these problems (I wouldn't like this!!!) and use your proposal, maybe with some modification that I would suggest

2.)  we introduce some elements like 'struct', 'array', 'list' and 'type' (all defined in the DTD) and use these elements to construct complex types, as you do it languages like C. Of course I have prepared a proposal for that :-).

If we go the second way, we also should revise the other elements and make some changes, for example the two listed above.


Other construction site:

To define things like sequences we could use a generic element 'property' in the following way:

<!ELEMENT sequence (property*)>
<!ATTLIST sequence 
                  name NMTOKEN #REQUIRED>

<!ELEMENT property EMPTY>
<!ATTLIST property
                   name NMTOKEN #REQUIRED
                   value NMTOKEN #REQURED>


Then you can define a sequence as follows:

<sequnce name="seq1">
   <property name="start" value="0"/>
   <property name="inc" value="1"/>
</sequence>


Intently waiting for your answer


Gerhard