Xerces bug XERCESJ-1687

I wish to share my anguish, that following Xerces bug has caused me:

https://issues.apache.org/jira/browse/XERCESJ-1687

The bug reporter is very right in his arguments. But somehow I've to say, the Xerces team cannot fix this bug right now. I've also been thinking to "resolve" this bug with a fix reason "later" (but my conscience doesn't allow that either).

I hope the situation will improve.

Zoomable Android image view

By default, an ImageView is not zoomable in an Android app by a finger touch. Just found a brilliant customization of Android's ImageView, which is zoomable. It's located here: https://github.com/MikeOrtiz/TouchImageView.

To use it in the app, we just have to do TouchImageView iv = (TouchImageView) findViewById(R.id.img); (in an Activity's onCreate method for example). Of course, TouchImageView supports all the behavior of standard ImageView class.

Mathematical table data with XML Schema 1.1

Here's a simple example, using XML Schema 1.1 <assert> to validate elementary school mathematical tables.

XML document:
<?xml version="1.0"?>
<table id="2">
  <x>2</x>
  <x>4</x>
  <x>6</x>
  <x>8</x>
  <x>10</x>
  <x>12</x>
  <x>14</x>
  <x>16</x>
  <x>18</x>
  <x>20</x>
</table>

XSD 1.1 document:
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
   <xs:element name="table">
     <xs:complexType>
        <xs:sequence>
           <xs:element name="x" minOccurs="10" maxOccurs="10"/>
        </xs:sequence>
        <xs:attribute name="id" type="xs:positiveInteger" use="required">
           <xs:annotation>
             <xs:documentation>Mathematical table of @id is represented.</xs:documentation>
           </xs:annotation>
        </xs:attribute>
        <xs:assert test="x[1] = @id"/>
        <xs:assert test="every $x in x[position() gt 1] satisfies $x = $x/preceding-sibling::x[1] + @id">
           <xs:annotation>
              <xs:documentation>An XPath 2.0 expression validating the depicted mathematical table.    
              </xs:documentation>
           </xs:annotation>
        </xs:assert>
     </xs:complexType>
   </xs:element>
 
</xs:schema>

Great write up on XML Schema 1.1

On this page, http://www.xfront.com/xml-schema-1-1/ Roger L. Costello has posted some wonderful write up on XML Schema 1.1 technology. Enthusiasts are encouraged to read that.

Roger's language is very simple, and covers almost everything from the perspective of XML Schema 1.1 user's needs.

XML Schema 1.1 inheritable attributes

I've been thinking to write a small and complete example, clarifying the role of XML Schema 1.1 inheritable attributes (please see inheritable = boolean within the definition "XML Representation Summary: attribute Element Information Item" in the XSD 1.1 specification).

The XSD 1.1 inheritable attributes, are primarily useful when implementing XSD Type Alternatives.

Below is an XSD 1.1 example, and two corresponding valid XML instance documents. This example as a whole implements inheritable attributes and few other areas of XSD 1.1.

XSD document:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
   <xs:element name="X">
      <xs:complexType>
         <xs:sequence>
            <xs:element name="Y">
               <xs:alternative test="@y = 'A'">
                  <xs:complexType>
                     <xs:sequence>
                        <xs:element name="A">
                           <xs:complexType>
                              <xs:simpleContent>
                                 <xs:extension base="xs:string">
                                    <xs:attribute name="attr" type="xs:integer"/>
                                 </xs:extension>
                              </xs:simpleContent>                            
                           </xs:complexType>
                        </xs:element>
                     </xs:sequence>
                  </xs:complexType>
               </xs:alternative>
               <xs:alternative test="@y = 'B'">
                 <xs:complexType>
                     <xs:sequence>
                        <xs:element name="B">
                           <xs:complexType>
                              <xs:simpleContent>
                                 <xs:extension base="xs:string">
                                    <xs:attribute name="attr" type="xs:integer"/>
                                 </xs:extension>
                              </xs:simpleContent>                            
                           </xs:complexType>
                        </xs:element>
                     </xs:sequence>
                  </xs:complexType>            
               </xs:alternative>
            </xs:element>
         </xs:sequence>
         <xs:attribute name="y" inheritable="true">
            <xs:simpleType>
               <xs:restriction base="xs:string">
                 <xs:enumeration value="A"/>
                 <xs:enumeration value="B"/>
               </xs:restriction>
            </xs:simpleType>
         </xs:attribute>
      </xs:complexType>
   </xs:element>
 
</xs:schema>


XML document 1:

<?xml version="1.0"?>
<X y="A">
  <Y>
    <A attr="1">hello</A>
  </Y>
</X>

XML document 2:

<?xml version="1.0"?>
<X y="B">
  <Y>
    <B attr="1">hello</B>
  </Y>
</X>

The XML instance documents shown above should be validated with the XSD document provided.

Following is little explanation with respect to the semantics of this example:
An inheritable attribute "y" is defined on element "X". The XSD type of element "Y" is chosen at runtime (i.e at validation time), depending on the value of this attribute. Please notice that, how an attribute defined on element "X" makes the definition of attribute accessible to element "Y" in the schema document.

I hope that, this blog post is useful.

XSLT 3.0 reaches W3C Recommendation status

Not long ago, XSLT 3.0 has reached the W3C Recommendation status. Below is the link to the XSLT 3.0 spec:

https://www.w3.org/TR/2017/REC-xslt-30-20170608/

XSLT 3.0 is a very advanced and useful language, as compared to XSLT 2.0. One of the main features (among others) introduced in XSLT 3.0, is that the XSLT transformation can be done in streaming mode.

XPath 2.0 atomization with XML Schema 1.1 validation

XPath 2.0 atomization as a concept, as applicable to XML Schema 1.1 validation is worth looking at. I would attempt to write something about this topic, here in this blog post.

Lets look at the following XML Schema 1.1 validation example, that we'll use to discuss this topic.

XSD 1.1 document:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
   <xs:element name="X">
      <xs:complexType>
         <xs:sequence>
            <xs:element name="a" type="xs:integer"/>
            <xs:element name="b" type="xs:integer"/>
         </xs:sequence>
         <xs:assert test="a gt b"/>
      </xs:complexType>
   </xs:element>
 
</xs:schema>

XML instance document that is validated with above mentioned XSD document:

<?xml version="1.0"?>
<X>
  <a>4</a>
  <b>7</b>
</X>

Upon XML Schema validation, the above mentioned XML instance document would be reported as invalid, because numeric value of "a" is less than "b". Now what is XPath 2.0 atomization, as for in this example that I wish to talk about?

Since the XML document has been validated with the mentioned XSD document, while building the XPath data model tree to evaluate <assert>, the nodes of XPath tree are bound with the XSD types as mentioned in the XSD document. Therefore, the <assert> XPath 2.0 expression "a gt b", comes with runtime availability of the corresponding XSD types on <assert> tree nodes for elements "a" and "b". In XPath 2.0 terms, the values as a result of atomization operation of nodes for XML elements "a" and "b" are used when an XPath expression "a gt b" is evaluated. We can't test a greater/less than relation on XML nodes, but we can do that on numbers for example, and the conversion of XML runtime nodes to atomic values like number is what XPath 2.0 atomization achieves.

I've used Apache Xerces as an XSD 1.1 validator, for testing examples for this blog post.

Turing Award 2016

Its nice to see, Sir Tim Berners-Lee as a recipient of A.M. Turing Award. More details are available on http://awards.acm.org/about/2016-turing.