Generating Restrictions in XML Schema Dynamically Using VB.NET 2005: Preliminaries

If you are new to XML, there exist several articles on XML alone on this web site (try “igrep”).  If you are new to XML Schema, I strongly suggest you go through my series “Designing your own XML Schema.”  If you are new to generating XML Schema using .NET, I suggest you go through my series “Generating XML schema dynamically using VB.NET 2005.”

The entire solution for this article was developed using Visual Studio 2005 Professional Edition on Windows Server 2003 standard edition. Some examples in this series may not compile successfully using Visual Studio 2003, as some of the features in .NET 1.1 turned out to be obsolete in .NET 2.0.  For complete details you can refer to this link: http://go.microsoft.com/fwlink/?linkid=14202.  Please  note that some of the examples in this series may not be practical.  Those were designed only for explaining the particular concept.

Restrictions (or constraints) in XML Schema: A sample schema

Since I already covered “restrictions” in my series “designing your own XML schema,” I will not repeat the information.  Here we shall work directly with a sample scenario.

I would like to have an element “AGE” present in my XML Schema.  I can assign a data type “integer” to it.  But this is not sufficient because I would like to have a value between 0 and 100 (whereas an integer would accept more than that).  This means a “restriction” is necessary.  Let us consider the following XML Schema, which can do something better:

Let us concentrate on the “age” element.  It stays under the “Employee” element.  Its “simpleType” (or data type) is defined as an integer type.  And finally, we applied the “restriction” by specifying the maximum value as follows:

You should also observe that “Name” and “Age” are defined with “simple types” rather than with “complex types.”  The only complex elements are “Organization” and “Employee.”  You can use “Exclusive” or “Inclusive” according to your requirements (they can even be interchanged).  But care should be taken while defining the same (especially when using tools).

Now let us go through an example with .NET!

Restrictions (or constraints) in XML Schema: VB.NET sample

In the previous section, I already listed a schema which we would like to generate dynamically.  The following is the complete VB.NET code to generate the previous schema:

I purposefully excluded the “import” statements, because I already covered them in my previous articles.  You can find a step-by-step explanation of the above code in the next section.

Restrictions (or constraints) in XML Schema: explanation

This section explains the code fragment listed in the previous section.  Let us examine it part by part.  I am excluding some of the parts which are already explained in previous articles. 

Since the “Employee” element itself is of the complex type, we can add any number of child elements to it.  Adding a “Name” element (child) to the “Employee” element looks like this:

And similarly I added another element, “Age,” as well.  After adding all the elements (or child elements) to the “Employee” element, we need to add the required attribute (which is “ID”).  The following code fragment shows how to add an attribute to a complex type of element:

And finally we need to focus on the restriction we applied to the XML schema.  The following is the main code fragment which implements the restriction. 

To apply the restriction, first of all we need to create a “simple type.”  The content of the simple type needs to be assigned with an object based on the “XmlSchemaSimpleTypeRestriction” class.  Within the above code fragment, I created an object “restriction” based on the same class and assigned it to the “content” property of the simple type. 

Any “restriction” is generally based on a certain base type and in this case, the base type would be an “integer” type.  Once the base type is fixed, we can now attach the appropriate facet for the restriction.  I used the “maxInclusive” facet which restricts based on the maximum value (inclusive of the value itself).  The maximum value to accept into the “Age” element is defined as “100.”  An acceptable XML document conforming to the above XML Schema would be as follows:

Extending the previous restriction with minExclusive

I gave an example covering the “Age” element previously.  It is not going to be a complete solution yet.  We specified only the maximum value (and forgot about the minimum value).  So, let us make tiny modifications (especially for the “Age” element) to our schema so that it looks like the following, which contains two facets now:

Within the above XML Schema, I managed to have two facets be implemented.  Now, with the above two facets we tightly restrict the “Age” element to have a value only between 1 and 100.  Now, let us see how we can achieve the same dynamically using .NET.

You can modify the code fragment presented in the previous sections as follows:

And that would achieve what we desired.  Once you execute the above code, you should be able to see the following output of the XML Schema:

Differences between xxxExclusive and xxxInclusive

This has caused a lot of confusion among several beginners when they design a new XML Schema.  Let us consider the following fragment of XML Schema:

According to the above code fragment, both values are “exclusive” during validation.  That means the “Age” element can have data between 2 and 99 (both inclusive) only.  Let us consider the following code fragment:

According to the above code fragment, both values are “inclusive” during validation.  That means the “Age” element can have data between 1 and 100 (both inclusive) only.  We can also mix them according to our necessity.  Let us consider the following code fragment:

According to the above code fragment, the “Age” element can have data between 2 and 100 (both inclusive) only.  Let us consider the following code fragment:

According to the above code fragment, the “Age” element can have data between 1 and 99 (both inclusive) only.

I hope the above examples clear up any confusion among the usage of “Inclusive” and “Exclusive” facets available when making restrictions in XML Schema.

The upcoming article will dig further into the details of restrictions using .NET.  So keep notified by signing up for a newsletter.  Any comments, suggestions, feedback, bugs, errors, enhancements are highly appreciated at jag_chat@yahoo.com