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Re: More L3 Core Comments

From: Curt Arnold <carnold@houston.rr.com>
Date: Mon, 11 Aug 2003 23:27:32 -0500
Message-ID: <3F386CB4.1060508@houston.rr.com>
To: Elena Litani <elitani@ca.ibm.com>, www-dom@w3.org

Elena Litani wrote:

>Hi Curt, 
>
>Thank you for your comments. 
>
>Curt Arnold wrote:
>  
>
>>Interface DOMImplementationSource:
>>
>>I dislike the form of this interface for a couple of reasons:  it
>>requires that each implementation source to parse the features list
>>which could have been done once for all implementation sources and it
>>enables the implementation source to return inconsistent first
>>implementation sources. 
>>    
>>
>
>I don't see how implementation may return inconsistent result..
>Can you give an example of the situation you are describing?
>
There are two distinct ways of getting the "first" implementation from a 
source.  For example, either:

DOMImplementation firstEvents = source.getDOMImplementation("Events")

or

DOMImplementation firstEvents = 
source.getDOMImplementations("Events").item(0);

could be used to get the first implementation of "Events" from a 
source.  It would be possible, but probably underdesirable and 
non-conformant, for these to return different objects. 

The Java definition of DOMImplementationRegistry does not call 
DOMImplementationSource.getDOMImplementations() so it would be very easy 
for an implementation of that method to have flaws that are not discovered.

The Java implementation of DOMImplementationRegistry would appear to be 
flawed since its implementation of getDOMImplementations() would only 
return the first implemention from each source.

>
>  
>
>>I'd suggest something like
>>interface DOMImplementationSource {
>>    DOMImplementation getDOMImplementation(DOMStringList features,
>>DOMStringList versions, unsigned int index);
>>}
>>    
>>
>
>Can you clarify your proposal, i.e. what is the purpose of index?
>
I'm assuming the motivation of the getDOMImplementation() was to avoid 
the creation of the list object and the item call when only the first 
implementation is of interest.  The index parameter is an attempt to 
still maintain those traits while also support multiple implementations 
per source without introducing a potential for inconsistency.  index = 0 
would return the first implementation, index = 1 the second, etc.  When 
the result was null, the list would be exhausted.

>Using your approach how would some one ask for an implementation that
>supports both "LS" and "Range" features?
>

A user or application would request an implementation in the same way, 
using the DOMImplementationRegistry, all that would be changing would be 
the interaction between the registry and a source.

DOMImplementation impl = 
DOMImplementationRegistry.newInstance().getDOMImplementation("LS 3.0 
Range");

What would change is that DOMImplementationRegistry would parse "LS 3.0 
Range" into

DOMStringList features = new DOMStringListImpl(new String[] { "LS", 
"Range" });
DOMStringList versions = new DOMStringListImpl(new String[] { "3.0", 
null } );

and then call

    source.getDOMImplementation(features, versions, 0);

DOMImplementationRegistry.getDOMImplementations() would do something like:


>Also, how can some one retrieve multiple DOM implementations if more
>than one available for the set of features specified?
>  
>

while(names.hasMoreElements()) {
            name = (String)names.nextElement();
            DOMImplementationSource source =
                (DOMImplementationSource) sources.get(name);

            for (int i = 0;; i++) {
                DOMImplementation impl = 
source.getDOMImplementation(features, versions, i);
                if (impl == null) break;
                list.add(impl);
            }


In the Java definition of DOMImplementationRegistry:

If multiple sources support the same feature set, the first 
implementation would be determined by the hash code of the source class 
name which would seem to be undesirable.

The use of a hashtable does prevent the same source name appearing in 
the list, however it would not prevent different sources from returning 
the same object.

I would suggest preserving the order of DOMImplementationSources and if 
it is necessary to eliminate duplicates do it in body of 
getDOMImplementations().
Received on Tuesday, 12 August 2003 00:27:35 GMT

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