Re: SDO - dealing with CDATA
On 08/11/06, Simon Laws <[EMAIL PROTECTED]> wrote: OK, so I've take my option 1 approach (see previous mail) and implemented a solution in C++ SDO which allows CDATA sections and their strange markers to appear in SDO properties. In this way the API for reading and creating CDATA sections is the normal SDO string API. In a way this is just a preliminary stab to allow us to play with CDATA and see whether this simple approach is satisfactory. From the previous mails there was discussion of alternative approaches where special markers are introduced to indicate where CDATA appears hence removing the need to maintain the CDATA markers in text. However there are some tricky cases. Particularly where one or more CDATA sections appear within primitive text string. As schema gives us no help in locating CDATA sections this leaves the model at a bit of a loss in terms of representing them. We would potentially end up adding scaffolding around primitive string types, or preferably create a new type, that is able to represent accurately the combination of text and CDATA sections. Anyhow something more complex may be appropriate in the future but this simple solution allows us to offer something to our PHP SDO users quickly that I don't think causes us big problems for the future. If in the future we have special flags we can always reproduce the CDATA markers if required. I created a JIRA to record progress on this issue ( http://issues.apache.org/jira/browse/TUSCANY-908) Simon Simon, I've looked through your patch and I think that's a sensible approach. It will obviously be a while (at least) before the specification has anything definitive to say on this subject and what you are doing at least gives the SDO user sight of the CDATA text. (Unlike the current situation where it is silently discarded.) Have you tried building your patch on Linux? Regards, Geoff.
Re: SDO - dealing with CDATA
On 11/3/06, Simon Laws <[EMAIL PROTECTED]> wrote:
On 11/3/06, Frank Budinsky <[EMAIL PROTECTED]> wrote:
>
> Simon,
>
> The Sequence entry returns a special property:
>
> if (sequence.getProperty(i) == specialCDataProperty) {
> String cDataValue = sequence.getValue(i);
> }
>
> The problem is that this special property is currently inherited from
> the
> underlying EMF, so it's really not something we want clients to use.
> RIght
> now, this works fine in terms of reading in CDATA and not losing it when
> you reserialize, but there's really no proper way for an SDO client to
> actually access it. Without using EMF apis, the only way a client can
> decide that an entry is CDATA is by looking at the property name (and
> hope
> there's no real property with that name). Longer term, I'm not sure that
>
> even handling it this way is right. Maybe CDATA and other special XML
> things should look like mixed text in the sequence (property == null),
> and
> some XMLHelper method (or some Tuscany specific API for now) could be
> used
> to check if it's actually something special like CDATA. Maybe you should
> try to do something like that in the C++ impl, and if it looks
> promissing,
> we'll switch the Java impl to do the same.
>
> Frank
>
> "Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 10:18:04
> AM:
>
> > On 11/3/06, Frank Budinsky <[EMAIL PROTECTED] > wrote:
> > >
> > > In the Tuscany Java implementation we expose CDATA as sequence
> entries
> > > (like mixed text) with a special "CDATA" property (we handle
> comments
> in a
> > > similar way). SDO doesn't define a special property for CDATA, so
> this
> is
> > > an implementation-specific feature. I'm not sure, long term, what
> should
> > > be the best (proper) way to do this.
> > >
> > > Frank.
> > >
> > > "Simon Laws" < [EMAIL PROTECTED]> wrote on 11/03/2006
> 09:41:25
> AM:
> > >
> > > > On 10/26/06, Simon Laws <[EMAIL PROTECTED] > wrote:
> > > > >
> > > > > This is primarily a C++ question but I guess could apply to Java
> also.
> > > I'm
> > > > > trying to read a document into C++ SDO that contains a CDATA
> section.
> > > The
> > > > > corresponding CDATA doesn't make its way into the resulting SDO.
> I
> put
> > > the
> > > > > C++ SDO implementation in the debugger and found the reason why:
>
> > > > >
> > > > > sax2parser.cpp
> > > > >
> > > > > void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
> > > > > {
> > > > > }
> > > > >
> > > > > So the callback exists, gets called with the correct data during
> the
> > > > > parse, i.e. LibXML2 is doing the right thing, but the callback
> is
> > > ignored.
> > > > > Is there a good reason for this? I did a quick search of the C++
> and
> > > Java
> > > > > specs and they don't appear to discuss CDATA specifically. Can
> someone
> > > > > comment on whether the Java implementation handles CDATA
> successfully?
> > > > >
> > > > > Logically, from an SDO point of view, there is probably no need
> to
> > > treat
> > > > > CDATA specially as the SDO model dictates precisely the
> difference
> > > between
> > > > > data and structure. We may find that to make the XML DAS
> function
> work
> > > we
> > > > > have to know that a property potentially contains markup but I'd
>
> have
> > > to
> > > > > look closely at how the C++ SDO implementation of the XML DAS
> function
> > > > > streams out SDOs to XML when requested to do so.
> > > > >
> > > > > If CDATA hasn't been omitted for a good reason I'll come up with
> a
> > > > > proposal for C++ SDO.
> > > > >
> > > > > Regards
> > > > >
> > > > > Simon
> > > >
> > > >
> > > >
> > > > I didn't get any response to this. Here are my further thoughts..
> > > >
> > > > There are a number of options for representing CDATA in SDO, for
> example
> > > >
> > > > 1) Duplicate the CDATA string as is, including the ""
> > > > markers, to the appropriate property in the data object hiearchy
> > > > 2) Duplicate the CDATA string excluding the ""
> > > markers
> > > > and instigate a special flag to indicate that CDATA is present.
> > > >
> > > > CDATA is the specific concern of XML, i.e. the chracter entities
> that
> > > CDATA
> > > > protects an XML parser from are of no
> > > > concern to SDO because SDO is not intended to be tied directly to
> XML.
> > > So
> > > > given the example options above we
> > > > either expose the specifics of XML to the SDO core 2) or to the
> SDO
> user
> > > 1).
> > > >
> > > > Neither are particularly attractive.
> > > >
> > > > 1) appears to be the simplest approach to implement because it
> provides
> > > a
> > > > mechanism for the user to read, and
> > > > create CDATA without having to provide much special support in
> SDO.
> 2)
> > > is
> > > > more involved particularly because
> > > > CDATA can appear mixed in with other text strings and so a
> sequence
> may
> > > need
> > > > to be used to represent properties
> > > > that have a mixture of text and CDATA marking those sequences
> entries
> > > that
> > > > are
Re: SDO - dealing with CDATA
On 11/3/06, Frank Budinsky <[EMAIL PROTECTED]> wrote:
Simon,
The Sequence entry returns a special property:
if (sequence.getProperty(i) == specialCDataProperty) {
String cDataValue = sequence.getValue(i);
}
The problem is that this special property is currently inherited from the
underlying EMF, so it's really not something we want clients to use. RIght
now, this works fine in terms of reading in CDATA and not losing it when
you reserialize, but there's really no proper way for an SDO client to
actually access it. Without using EMF apis, the only way a client can
decide that an entry is CDATA is by looking at the property name (and hope
there's no real property with that name). Longer term, I'm not sure that
even handling it this way is right. Maybe CDATA and other special XML
things should look like mixed text in the sequence (property == null), and
some XMLHelper method (or some Tuscany specific API for now) could be used
to check if it's actually something special like CDATA. Maybe you should
try to do something like that in the C++ impl, and if it looks promissing,
we'll switch the Java impl to do the same.
Frank
"Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 10:18:04 AM:
> On 11/3/06, Frank Budinsky <[EMAIL PROTECTED]> wrote:
> >
> > In the Tuscany Java implementation we expose CDATA as sequence entries
> > (like mixed text) with a special "CDATA" property (we handle comments
in a
> > similar way). SDO doesn't define a special property for CDATA, so this
is
> > an implementation-specific feature. I'm not sure, long term, what
should
> > be the best (proper) way to do this.
> >
> > Frank.
> >
> > "Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 09:41:25
AM:
> >
> > > On 10/26/06, Simon Laws <[EMAIL PROTECTED]> wrote:
> > > >
> > > > This is primarily a C++ question but I guess could apply to Java
also.
> > I'm
> > > > trying to read a document into C++ SDO that contains a CDATA
section.
> > The
> > > > corresponding CDATA doesn't make its way into the resulting SDO. I
put
> > the
> > > > C++ SDO implementation in the debugger and found the reason why:
> > > >
> > > > sax2parser.cpp
> > > >
> > > > void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
> > > > {
> > > > }
> > > >
> > > > So the callback exists, gets called with the correct data during
the
> > > > parse, i.e. LibXML2 is doing the right thing, but the callback is
> > ignored.
> > > > Is there a good reason for this? I did a quick search of the C++
and
> > Java
> > > > specs and they don't appear to discuss CDATA specifically. Can
someone
> > > > comment on whether the Java implementation handles CDATA
successfully?
> > > >
> > > > Logically, from an SDO point of view, there is probably no need to
> > treat
> > > > CDATA specially as the SDO model dictates precisely the difference
> > between
> > > > data and structure. We may find that to make the XML DAS function
work
> > we
> > > > have to know that a property potentially contains markup but I'd
have
> > to
> > > > look closely at how the C++ SDO implementation of the XML DAS
function
> > > > streams out SDOs to XML when requested to do so.
> > > >
> > > > If CDATA hasn't been omitted for a good reason I'll come up with a
> > > > proposal for C++ SDO.
> > > >
> > > > Regards
> > > >
> > > > Simon
> > >
> > >
> > >
> > > I didn't get any response to this. Here are my further thoughts..
> > >
> > > There are a number of options for representing CDATA in SDO, for
example
> > >
> > > 1) Duplicate the CDATA string as is, including the ""
> > > markers, to the appropriate property in the data object hiearchy
> > > 2) Duplicate the CDATA string excluding the ""
> > markers
> > > and instigate a special flag to indicate that CDATA is present.
> > >
> > > CDATA is the specific concern of XML, i.e. the chracter entities
that
> > CDATA
> > > protects an XML parser from are of no
> > > concern to SDO because SDO is not intended to be tied directly to
XML.
> > So
> > > given the example options above we
> > > either expose the specifics of XML to the SDO core 2) or to the SDO
user
> > 1).
> > >
> > > Neither are particularly attractive.
> > >
> > > 1) appears to be the simplest approach to implement because it
provides
> > a
> > > mechanism for the user to read, and
> > > create CDATA without having to provide much special support in SDO.
2)
> > is
> > > more involved particularly because
> > > CDATA can appear mixed in with other text strings and so a sequence
may
> > need
> > > to be used to represent properties
> > > that have a mixture of text and CDATA marking those sequences
entries
> > that
> > > are CDATA.
> > >
> > > 1) does require changes (at least in C++ SDO) because XML parsers
tend
> > to be
> > > too helpful in this case for
> > > processing CDATA. XML parsers, libxml2 in particular, recognize the
> > > "" sequence as a special
> > > indicator and throw it away returning just the text it includes. We
> > would
> > > have to reintroduce it and store it in
>
Re: SDO - dealing with CDATA
Simon,
The Sequence entry returns a special property:
if (sequence.getProperty(i) == specialCDataProperty) {
String cDataValue = sequence.getValue(i);
}
The problem is that this special property is currently inherited from the
underlying EMF, so it's really not something we want clients to use. RIght
now, this works fine in terms of reading in CDATA and not losing it when
you reserialize, but there's really no proper way for an SDO client to
actually access it. Without using EMF apis, the only way a client can
decide that an entry is CDATA is by looking at the property name (and hope
there's no real property with that name). Longer term, I'm not sure that
even handling it this way is right. Maybe CDATA and other special XML
things should look like mixed text in the sequence (property == null), and
some XMLHelper method (or some Tuscany specific API for now) could be used
to check if it's actually something special like CDATA. Maybe you should
try to do something like that in the C++ impl, and if it looks promissing,
we'll switch the Java impl to do the same.
Frank
"Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 10:18:04 AM:
> On 11/3/06, Frank Budinsky <[EMAIL PROTECTED]> wrote:
> >
> > In the Tuscany Java implementation we expose CDATA as sequence entries
> > (like mixed text) with a special "CDATA" property (we handle comments
in a
> > similar way). SDO doesn't define a special property for CDATA, so this
is
> > an implementation-specific feature. I'm not sure, long term, what
should
> > be the best (proper) way to do this.
> >
> > Frank.
> >
> > "Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 09:41:25
AM:
> >
> > > On 10/26/06, Simon Laws <[EMAIL PROTECTED]> wrote:
> > > >
> > > > This is primarily a C++ question but I guess could apply to Java
also.
> > I'm
> > > > trying to read a document into C++ SDO that contains a CDATA
section.
> > The
> > > > corresponding CDATA doesn't make its way into the resulting SDO. I
put
> > the
> > > > C++ SDO implementation in the debugger and found the reason why:
> > > >
> > > > sax2parser.cpp
> > > >
> > > > void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
> > > > {
> > > > }
> > > >
> > > > So the callback exists, gets called with the correct data during
the
> > > > parse, i.e. LibXML2 is doing the right thing, but the callback is
> > ignored.
> > > > Is there a good reason for this? I did a quick search of the C++
and
> > Java
> > > > specs and they don't appear to discuss CDATA specifically. Can
someone
> > > > comment on whether the Java implementation handles CDATA
successfully?
> > > >
> > > > Logically, from an SDO point of view, there is probably no need to
> > treat
> > > > CDATA specially as the SDO model dictates precisely the difference
> > between
> > > > data and structure. We may find that to make the XML DAS function
work
> > we
> > > > have to know that a property potentially contains markup but I'd
have
> > to
> > > > look closely at how the C++ SDO implementation of the XML DAS
function
> > > > streams out SDOs to XML when requested to do so.
> > > >
> > > > If CDATA hasn't been omitted for a good reason I'll come up with a
> > > > proposal for C++ SDO.
> > > >
> > > > Regards
> > > >
> > > > Simon
> > >
> > >
> > >
> > > I didn't get any response to this. Here are my further thoughts..
> > >
> > > There are a number of options for representing CDATA in SDO, for
example
> > >
> > > 1) Duplicate the CDATA string as is, including the ""
> > > markers, to the appropriate property in the data object hiearchy
> > > 2) Duplicate the CDATA string excluding the ""
> > markers
> > > and instigate a special flag to indicate that CDATA is present.
> > >
> > > CDATA is the specific concern of XML, i.e. the chracter entities
that
> > CDATA
> > > protects an XML parser from are of no
> > > concern to SDO because SDO is not intended to be tied directly to
XML.
> > So
> > > given the example options above we
> > > either expose the specifics of XML to the SDO core 2) or to the SDO
user
> > 1).
> > >
> > > Neither are particularly attractive.
> > >
> > > 1) appears to be the simplest approach to implement because it
provides
> > a
> > > mechanism for the user to read, and
> > > create CDATA without having to provide much special support in SDO.
2)
> > is
> > > more involved particularly because
> > > CDATA can appear mixed in with other text strings and so a sequence
may
> > need
> > > to be used to represent properties
> > > that have a mixture of text and CDATA marking those sequences
entries
> > that
> > > are CDATA.
> > >
> > > 1) does require changes (at least in C++ SDO) because XML parsers
tend
> > to be
> > > too helpful in this case for
> > > processing CDATA. XML parsers, libxml2 in particular, recognize the
> > > "" sequence as a special
> > > indicator and throw it away returning just the text it includes. We
> > would
> > > have to reintroduce it and store it in
> > > the parameter valu
Re: SDO - dealing with CDATA
On 11/3/06, Frank Budinsky <[EMAIL PROTECTED]> wrote:
In the Tuscany Java implementation we expose CDATA as sequence entries
(like mixed text) with a special "CDATA" property (we handle comments in a
similar way). SDO doesn't define a special property for CDATA, so this is
an implementation-specific feature. I'm not sure, long term, what should
be the best (proper) way to do this.
Frank.
"Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 09:41:25 AM:
> On 10/26/06, Simon Laws <[EMAIL PROTECTED]> wrote:
> >
> > This is primarily a C++ question but I guess could apply to Java also.
I'm
> > trying to read a document into C++ SDO that contains a CDATA section.
The
> > corresponding CDATA doesn't make its way into the resulting SDO. I put
the
> > C++ SDO implementation in the debugger and found the reason why:
> >
> > sax2parser.cpp
> >
> > void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
> > {
> > }
> >
> > So the callback exists, gets called with the correct data during the
> > parse, i.e. LibXML2 is doing the right thing, but the callback is
ignored.
> > Is there a good reason for this? I did a quick search of the C++ and
Java
> > specs and they don't appear to discuss CDATA specifically. Can someone
> > comment on whether the Java implementation handles CDATA successfully?
> >
> > Logically, from an SDO point of view, there is probably no need to
treat
> > CDATA specially as the SDO model dictates precisely the difference
between
> > data and structure. We may find that to make the XML DAS function work
we
> > have to know that a property potentially contains markup but I'd have
to
> > look closely at how the C++ SDO implementation of the XML DAS function
> > streams out SDOs to XML when requested to do so.
> >
> > If CDATA hasn't been omitted for a good reason I'll come up with a
> > proposal for C++ SDO.
> >
> > Regards
> >
> > Simon
>
>
>
> I didn't get any response to this. Here are my further thoughts..
>
> There are a number of options for representing CDATA in SDO, for example
>
> 1) Duplicate the CDATA string as is, including the ""
> markers, to the appropriate property in the data object hiearchy
> 2) Duplicate the CDATA string excluding the ""
markers
> and instigate a special flag to indicate that CDATA is present.
>
> CDATA is the specific concern of XML, i.e. the chracter entities that
CDATA
> protects an XML parser from are of no
> concern to SDO because SDO is not intended to be tied directly to XML.
So
> given the example options above we
> either expose the specifics of XML to the SDO core 2) or to the SDO user
1).
>
> Neither are particularly attractive.
>
> 1) appears to be the simplest approach to implement because it provides
a
> mechanism for the user to read, and
> create CDATA without having to provide much special support in SDO. 2)
is
> more involved particularly because
> CDATA can appear mixed in with other text strings and so a sequence may
need
> to be used to represent properties
> that have a mixture of text and CDATA marking those sequences entries
that
> are CDATA.
>
> 1) does require changes (at least in C++ SDO) because XML parsers tend
to be
> too helpful in this case for
> processing CDATA. XML parsers, libxml2 in particular, recognize the
> "" sequence as a special
> indicator and throw it away returning just the text it includes. We
would
> have to reintroduce it and store it in
> the parameter value in question. The C++ SDO implementation uses a lot
of
> XML string handling before the parameter
> value is actually stored which URL encodes parts of the CDATA markers so
> this would have to be fixed. When writing out the CDATA strings any
string
> typed properties would have to be scanned for the markers so that the
> appropriate libxml2 functions can be called to get the CDATA sections in
the
> right place.
>
> I have a test implementation of 1). If this is the way we want to go I
would
> have to do more work to thread CDATA handling through the xml strings
that
> are used to set parameters. Happy to do this but would like to discuss
> first.
>
> Thoughts (particularly on what Java SDO does with CDATA)?
>
> Simon
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Ok, thanks for that Frank. It would be nice for us to do it in the same
way so even though it is not in the SDO spec the implementations are
similar. A question, how do you set a sequence entry to indicate that it
holds CDATA. Is this a flag that is exposed on the sequence API. I'm not
really familiar with the Java SDO code base. Can you give me a class name to
go look at?
Simon
Re: SDO - dealing with CDATA
In the Tuscany Java implementation we expose CDATA as sequence entries
(like mixed text) with a special "CDATA" property (we handle comments in a
similar way). SDO doesn't define a special property for CDATA, so this is
an implementation-specific feature. I'm not sure, long term, what should
be the best (proper) way to do this.
Frank.
"Simon Laws" <[EMAIL PROTECTED]> wrote on 11/03/2006 09:41:25 AM:
> On 10/26/06, Simon Laws <[EMAIL PROTECTED]> wrote:
> >
> > This is primarily a C++ question but I guess could apply to Java also.
I'm
> > trying to read a document into C++ SDO that contains a CDATA section.
The
> > corresponding CDATA doesn't make its way into the resulting SDO. I put
the
> > C++ SDO implementation in the debugger and found the reason why:
> >
> > sax2parser.cpp
> >
> > void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
> > {
> > }
> >
> > So the callback exists, gets called with the correct data during the
> > parse, i.e. LibXML2 is doing the right thing, but the callback is
ignored.
> > Is there a good reason for this? I did a quick search of the C++ and
Java
> > specs and they don't appear to discuss CDATA specifically. Can someone
> > comment on whether the Java implementation handles CDATA successfully?
> >
> > Logically, from an SDO point of view, there is probably no need to
treat
> > CDATA specially as the SDO model dictates precisely the difference
between
> > data and structure. We may find that to make the XML DAS function work
we
> > have to know that a property potentially contains markup but I'd have
to
> > look closely at how the C++ SDO implementation of the XML DAS function
> > streams out SDOs to XML when requested to do so.
> >
> > If CDATA hasn't been omitted for a good reason I'll come up with a
> > proposal for C++ SDO.
> >
> > Regards
> >
> > Simon
>
>
>
> I didn't get any response to this. Here are my further thoughts..
>
> There are a number of options for representing CDATA in SDO, for example
>
> 1) Duplicate the CDATA string as is, including the ""
> markers, to the appropriate property in the data object hiearchy
> 2) Duplicate the CDATA string excluding the ""
markers
> and instigate a special flag to indicate that CDATA is present.
>
> CDATA is the specific concern of XML, i.e. the chracter entities that
CDATA
> protects an XML parser from are of no
> concern to SDO because SDO is not intended to be tied directly to XML.
So
> given the example options above we
> either expose the specifics of XML to the SDO core 2) or to the SDO user
1).
>
> Neither are particularly attractive.
>
> 1) appears to be the simplest approach to implement because it provides
a
> mechanism for the user to read, and
> create CDATA without having to provide much special support in SDO. 2)
is
> more involved particularly because
> CDATA can appear mixed in with other text strings and so a sequence may
need
> to be used to represent properties
> that have a mixture of text and CDATA marking those sequences entries
that
> are CDATA.
>
> 1) does require changes (at least in C++ SDO) because XML parsers tend
to be
> too helpful in this case for
> processing CDATA. XML parsers, libxml2 in particular, recognize the
> "" sequence as a special
> indicator and throw it away returning just the text it includes. We
would
> have to reintroduce it and store it in
> the parameter value in question. The C++ SDO implementation uses a lot
of
> XML string handling before the parameter
> value is actually stored which URL encodes parts of the CDATA markers so
> this would have to be fixed. When writing out the CDATA strings any
string
> typed properties would have to be scanned for the markers so that the
> appropriate libxml2 functions can be called to get the CDATA sections in
the
> right place.
>
> I have a test implementation of 1). If this is the way we want to go I
would
> have to do more work to thread CDATA handling through the xml strings
that
> are used to set parameters. Happy to do this but would like to discuss
> first.
>
> Thoughts (particularly on what Java SDO does with CDATA)?
>
> Simon
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
Re: SDO - dealing with CDATA
On 10/26/06, Simon Laws <[EMAIL PROTECTED]> wrote:
This is primarily a C++ question but I guess could apply to Java also. I'm
trying to read a document into C++ SDO that contains a CDATA section. The
corresponding CDATA doesn't make its way into the resulting SDO. I put the
C++ SDO implementation in the debugger and found the reason why:
sax2parser.cpp
void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
{
}
So the callback exists, gets called with the correct data during the
parse, i.e. LibXML2 is doing the right thing, but the callback is ignored.
Is there a good reason for this? I did a quick search of the C++ and Java
specs and they don't appear to discuss CDATA specifically. Can someone
comment on whether the Java implementation handles CDATA successfully?
Logically, from an SDO point of view, there is probably no need to treat
CDATA specially as the SDO model dictates precisely the difference between
data and structure. We may find that to make the XML DAS function work we
have to know that a property potentially contains markup but I'd have to
look closely at how the C++ SDO implementation of the XML DAS function
streams out SDOs to XML when requested to do so.
If CDATA hasn't been omitted for a good reason I'll come up with a
proposal for C++ SDO.
Regards
Simon
I didn't get any response to this. Here are my further thoughts..
There are a number of options for representing CDATA in SDO, for example
1) Duplicate the CDATA string as is, including the ""
markers, to the appropriate property in the data object hiearchy
2) Duplicate the CDATA string excluding the "" markers
and instigate a special flag to indicate that CDATA is present.
CDATA is the specific concern of XML, i.e. the chracter entities that CDATA
protects an XML parser from are of no
concern to SDO because SDO is not intended to be tied directly to XML. So
given the example options above we
either expose the specifics of XML to the SDO core 2) or to the SDO user 1).
Neither are particularly attractive.
1) appears to be the simplest approach to implement because it provides a
mechanism for the user to read, and
create CDATA without having to provide much special support in SDO. 2) is
more involved particularly because
CDATA can appear mixed in with other text strings and so a sequence may need
to be used to represent properties
that have a mixture of text and CDATA marking those sequences entries that
are CDATA.
1) does require changes (at least in C++ SDO) because XML parsers tend to be
too helpful in this case for
processing CDATA. XML parsers, libxml2 in particular, recognize the
"" sequence as a special
indicator and throw it away returning just the text it includes. We would
have to reintroduce it and store it in
the parameter value in question. The C++ SDO implementation uses a lot of
XML string handling before the parameter
value is actually stored which URL encodes parts of the CDATA markers so
this would have to be fixed. When writing out the CDATA strings any string
typed properties would have to be scanned for the markers so that the
appropriate libxml2 functions can be called to get the CDATA sections in the
right place.
I have a test implementation of 1). If this is the way we want to go I would
have to do more work to thread CDATA handling through the xml strings that
are used to set parameters. Happy to do this but would like to discuss
first.
Thoughts (particularly on what Java SDO does with CDATA)?
Simon
SDO - dealing with CDATA
This is primarily a C++ question but I guess could apply to Java also. I'm
trying to read a document into C++ SDO that contains a CDATA section. The
corresponding CDATA doesn't make its way into the resulting SDO. I put the
C++ SDO implementation in the debugger and found the reason why:
sax2parser.cpp
void sdo_cdataBlock(void *ctx, const xmlChar *value, int len)
{
}
So the callback exists, gets called with the correct data during the parse,
i.e. LibXML2 is doing the right thing, but the callback is ignored. Is there
a good reason for this? I did a quick search of the C++ and Java specs and
they don't appear to discuss CDATA specifically. Can someone comment on
whether the Java implementation handles CDATA successfully?
Logically, from an SDO point of view, there is probably no need to treat
CDATA specially as the SDO model dictates precisely the difference between
data and structure. We may find that to make the XML DAS function work we
have to know that a property potentially contains markup but I'd have to
look closely at how the C++ SDO implementation of the XML DAS function
streams out SDOs to XML when requested to do so.
If CDATA hasn't been omitted for a good reason I'll come up with a proposal
for C++ SDO.
Regards
Simon
