R – Should I learn XML before WCF

wcfweb servicesxml

a) I plan to start learning WCF, but I’m not sure whether it’s important to learn XML first. If XML should be learned before WCF, why?

b) In case XML should be learned prior to WCF, then I’d prefer to learn just the parts required to understand WCF. So which of the following XML technologies should be tackled and in how much detail:

basics of XML
DTD
XML schemas
XPath
XSLT
XQuery

thanx

Best Answer

Fundamental Fact: Learning XML in a stand-alone manner does not make sense because XML is not used in a stand-alone manner.

Since, you are about to learn WCF, I would suggest you to get a hang of WebServices first. That way you will learn the basics you want to learn about XML and also its relevance as a choice for serialized data transfer.

Also, it would make sense to learn about the various advantages and options provided in SQL Server for XML support.

So, learn XML in conjunction with a relevant technology that would prove more useful to you.

XML escape characters

There are only five:

"   &quot;
'   &apos;
<   &lt;
>   &gt;
&   &amp;

Escaping characters depends on where the special character is used.

The examples can be validated at the W3C Markup Validation Service.

Text

The safe way is to escape all five characters in text. However, the three characters ", ' and > needn't be escaped in text:

<?xml version="1.0"?>
<valid>"'></valid>

Attributes

The safe way is to escape all five characters in attributes. However, the > character needn't be escaped in attributes:

<?xml version="1.0"?>
<valid attribute=">"/>

The ' character needn't be escaped in attributes if the quotes are ":

<?xml version="1.0"?>
<valid attribute="'"/>

Likewise, the " needn't be escaped in attributes if the quotes are ':

<?xml version="1.0"?>
<valid attribute='"'/>

Comments

All five special characters must not be escaped in comments:

<?xml version="1.0"?>
<valid>
<!-- "'<>& -->
</valid>

CDATA

All five special characters must not be escaped in CDATA sections:

<?xml version="1.0"?>
<valid>
<![CDATA["'<>&]]>
</valid>

Processing instructions

All five special characters must not be escaped in XML processing instructions:

<?xml version="1.0"?>
<?process <"'&> ?>
<valid/>

XML vs. HTML

HTML has its own set of escape codes which cover a lot more characters.

Python – How to parse XML and count instances of a particular node attribute

I suggest ElementTree. There are other compatible implementations of the same API, such as lxml, and cElementTree in the Python standard library itself; but, in this context, what they chiefly add is even more speed -- the ease of programming part depends on the API, which ElementTree defines.

First build an Element instance root from the XML, e.g. with the XML function, or by parsing a file with something like:

import xml.etree.ElementTree as ET
root = ET.parse('thefile.xml').getroot()

Or any of the many other ways shown at ElementTree. Then do something like:

for type_tag in root.findall('bar/type'):
    value = type_tag.get('foobar')
    print(value)

And similar, usually pretty simple, code patterns.