It's been rumoured that Christopher Browne said:
>
> > Here's the question: if one writes a soap dtd/schema in the M$
> > framework, it will then auto-generate language bindings for several
> > languages? (i.e. they treat the soap dtd/schema as an IDL for
> > all practical purposes? OR did they invent some new IDL language?)
>
> None of the above.
>
> What SOAP amounts to....
Right, but that doesn't answer the question. Marshalling and message
formats are related to language bindings, but are not the same thing.
For example, If I were building a system like this, and this were
C++, I might build a base class like so:
class XML_IO_Base_Class {
public:
void SendMyself (); // converts object to XML and
// sends it on socket
void ReceiveMyself(); // receives XML from socket, and
// populates object field values
private:
int socket; // etc ...
};
And anything deriving from this can send/receive itself over the net:
e.g.
class gnc_account : public XML_IO_Base_Class {
public:
char * account_name;
char * bank_name;
int current_balance;
}
So, to send the account struct accross the net, we do:
gnc_account *acc = new gnc_account;
acc->account_name = "ABC Credit Line";
acc->current_balance=100;
acc->SendMyself();
The problem is, of course, that XML_IO_Base_Class needs to 'find out'
or 'know', somehow, that gnc_account consists of three fields, two
of which are char *, and one of which is int.
In CORBA and RPC, a description of the structure is accomplished with
an IDL; then IDL parsers generate 'stubs' that automatically
implement routines such as "SendMyself()".
Note that XML DTD's contain *almost* enough information to be an IDL,
but not quite. In particular, they fail to indicate the type of
the field.
For example:
<gnc_account>
<account_name>ABC Credit Line</account_name>
<current_balance>100</current_balance>
</gnc_account>
has a dtd that looks like
<!element gnc_account - - (account_name, current_balance)>
<!element account_name - o #PCDATA>
<!element current_balance - o #PCDATA>
Sooo ... is the balance an int or a char *? The DTD doesn't say,
can't say.
This isn't a problem for perl, because perl 'doesn't have' types.
$account_balance = "100"; # string? number? no problem in perl
I don't know C# or VB, but maybe they're untyped as well. But for
C and C++, and Java, its a problem.
Sooo I restate the question: Does Microsoft define a new IDL
language to deal with this issue, or do they extend the idea of a DTD
to indicate the type in some way, e.g. OFX is marked up in the
following rather bogus fashion:
<!-- four byte integer -->
<!ENTITY % INTTYPE "(#PCDATA)">
<!--#ENTITY % INTTYPE #Datatype(I-4)-->
<!-- string of 255 chars or less, BSOD if more -->
<!ENTITY % CHARTYPE "(#PCDATA)">
<!--#ENTITY % CHARTYPE #Datatype(A-255)-->
---------
Either SOAP / .net needs to solve this problem for typed languages,
or everybody should program in perl. I'm curious about how this is
handled.
--linas
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