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RE: ConciseXML syntax

  • To: "Mike Plusch" <mplusch@c...>,<xml-dev@l...>
  • Subject: RE: ConciseXML syntax
  • From: "Dare Obasanjo" <dareo@m...>
  • Date: Fri, 17 Jan 2003 12:06:53 -0800
  • Thread-index: AcK+Yq8U1vAZCXuFSvO0xvZiKJdClAAAPG9A
  • Thread-topic: ConciseXML syntax

meaning of the xml data
Not only do you make outlandish claims but you overempasize what are
irrelevant issues as serious problems. 

PS: XML can't represent objects at best it can represent C-style structs
and even then it needs a notion of IDness to do this completely. 

-- 
PITHY WORDS OF WISDOM 
A pipe gives a wise man time to think and a fool something to stick in
his mouth.                           

This posting is provided "AS IS" with no warranties, and confers no
rights. 

>  
>  
> -----Original Message-----
> From: Mike Plusch [mailto:mplusch@c...] 
> Sent: Friday, January 17, 2003 11:57 AM
> To: xml-dev@l...
> 
> 
> ----- Original Message -----
> From: "Rodriguez, Sergio" <srodriguez@c...>
> 
> >I've always assumed that "compatible with XML" meant  "would pass 
> >through an XML 1.0 parser without a fatal error".
> 
> I say that a standard "uses the XML 1.0 syntax".
> Compatibility usually implies that one thing can be used 
> instead of another thing.  You wouldn't say that XHTML could 
> be used instead of XML -- it's comparing different things.
> I think it is confusing if you say that XHTML is compatible 
> with XML.  A vocabulary using XML syntax is much different 
> that a syntax.
> 
> Mike Plush wrote:
> >If you ask 5 developers to create an XML 1.0 representation for a 
> >single, well-specific object (say a Java object), then you 
> will likely 
> >get 5 _different_ XML 1.0 representations for that same 
> object.  This 
> >is a HUGE problem that leads to a lot of semantic ambiguity. 
> ConciseXML 
> >has no such problem.
> 
> Sergio Rodriguez wrote:
> >How can this be?  Any examples of how "ConciseXML" resolves the
> semantic
> >ambiguity problem of the abstraction of any entity?
> 
> Sure.  I'll take a section from Chapter 2 of my Water book.
> 
> XML is commonly used to represent data structures. A data 
> structure is just a way to represent data that obeys some 
> well-defined structure. I will describe how Water can 
> formally describe the structure of data by using Water Type 
> and Water Contract. But this chapter shows how to 
> unambiguously represent static data by using Water.
> 
> Representing static data might seem straightforward, but XML 
> 1.0 has some design constraints carried over from the 
> document markup world that make representing data in XML 
> quite confusing. A discussion about elements versus 
> attributes is a common example of this confusion.
> In most programming languages and other technologies for 
> representing data, there is a concept of a data structure, 
> data value, or object. This book, by convention, will use the 
> term object. The word object will be similar to other terms 
> such as a record, structure, or tuple from other technologies.
> 
> In most programming languages, an object has fields, and 
> those fields hold values that are other objects. Water 
> objects have this property as well. An object is a collection 
> of fields. Each field has a key and a value. The value can be 
> any object.
> 
> The following is an example of an item object.
> <item id="XL283 " color=="blue " size==10/>
> 
> The preceding XML could be verbally described as creating an 
> instance of an item object. The instance has three fields: id 
> , color , and size . The value of the id field is the string 
> "XL283 ", the value of the color field is "blue ", and the 
> value of the size field is the number 10 .
> 
> The type or class of the object appears as the element's 
> name, immediately following the opening angle bracket (<). 
> The fields of the object are represented as key-value pairs 
> within the element's opening area.
> 
> When you see an opening angle bracket, it syntactically is 
> the start of an XML element, but it has the semantic meaning 
> of performing a call. The call is either the calling of 
> method, or the calling of a constructor method of an object. 
> Fields of an object have a clear and unambiguous key and value.
> 
> <item id="xx283 " color=="blue " size==10/>
> 
> In the preceding line, the instance of item has three fields. 
> "id "is the key of the first field, and "xx283 "is the value 
> of the field. "color "is the key of the second field and 
> "blue "is its value. "size "is the key of the third field and 
> the integer 10 is its value.
> 
> It is very common, though, to see the following XML to 
> represent the instance of item above.
> <item>
> <id>xx283</id>
> <color>blue</color>
> <size>10</size>
> </item>
> 
> To the vast majority of people, the above XML looks very 
> normal and easily understood, but this is an example of XML 
> in the flat-world model. The round-world model sees this as 
> an ambiguous, poorly constructed XML data object.
> One
> problem that is described in detail later in this chapter is 
> that the syntax of an XML element is used to represent two 
> very different things: an object and a field of an object. 
> Having one syntax to represent two different concepts 
> presents a serious ambiguity. This ambiguity leads to a 
> serious problem when a machine tries to interpret the meaning 
> of the XML data.
> 
> For a data structure to be useful, the distinction between 
> objects and fields is extremely important. How, for example, 
> do you know that <color>blue</color> represents a field of 
> item and not an instance of type color ? As humans, we use 
> our gift of pattern recognition to deduce that color must be 
> a field of item because it occurs within the content of item 
> and it has blue in the content of the element.
> To emphasize the ambiguity, what if you wrapped the item 
> within another color element? Is item now a field of color ? 
> Did the meaning of item radically change because it moved to 
> a different level in the structure?
> 
> <color>
> <item>
> <id>xx283</id>
> <color>blue</color>
> <size>10</size>
> </item>
> </color>
> 
> If a serious ambiguity appears in such a small example, 
> imagine the scope of the problem when objects and data 
> structures get more complex. At a minimum, data structures 
> need to be unambiguous and not depend on any other knowledge 
> for interpreting a data structure.
> 
> Most XML examples today exhibit the problem of element 
> ambiguity where elements are used for both representing a 
> field of an object as well as objects themselves. The problem 
> occurs in most XML standards and text-book examples from 
> major publishers. It is so common, in fact, that it is almost 
> impossible to find XML examples that do not have this problem.
> I
> believe that the "object-field ambiguity" of XML is one of 
> the primary reasons why XML is much more complex than 
> necessary. This widespread problem is one of the reasons for 
> the slow pace of XML adoption.
> 
> Water's use of XML makes a clear separation between objects 
> and fields. An XML element represents an object. XML 
> attributes represent fields of an object. The ConciseXML 
> syntax allows any type of object as the value of an 
> attribute; therefore, Water supports fields that can store 
> any type of object -not just strings.
> 
> 
> 
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