XML Interview Questions and Answers

Are the names of all element types and attributes in some XML namespace?

No.
If an element type or attribute name is not specifically declared to be in an XML namespace -- that is, it is unprefixed and (in the case of element type names) there is no default XML namespace -- then that name is not in any XML namespace. If you want, you can think of it as having a null URI as its name, although no "null" XML namespace actually exists. For example, in the following, the element type name B and the attribute names C and E are not in any XML namespace:
<google:A xmlns:google="http://www.google.org/">
<B C="bar"/>
<google:D E="bar"/>
</google:A>

Do XML namespaces apply to entity names, notation names, or processing instruction targets?

No.
XML namespaces apply only to element type and attribute names. Furthermore, in an XML document that conforms to the XML namespaces recommendation, entity names, notation names, and processing instruction targets must not contain colons.

Who can create an XML namespace?

Anybody can create an XML namespace -- all you need to do is assign a URI as its name and decide what element type and attribute names are in it. The URI must be under your control and should not be being used to identify a different XML namespace, such as by a coworker.
(In practice, most people that create XML namespaces also describe the element types and attributes whose names are in it -- their content models and types, their semantics, and so on. However, this is not part of the process of creating an XML namespace, nor does the XML namespace include or provide a way to discover such information.)

Do I need to use XML namespaces?

Maybe, maybe not.
If you don't have any naming conflicts in the XML documents you are using today, as is often the case with documents used inside a single organization, then you probably don't need to use XML namespaces. However, if you do have conflicts today, or if you expect conflicts in the future due to distributing your documents outside your organization or bringing outside documents into your organization, then you should probably use XML namespaces.
Regardless of whether you use XML namespaces in your own documents, it is likely that you will use them in conjunction with some other XML technology, such as XSL, XHTML, or XML Schemas. For example, the following XSLT (XSL Transformations) stylesheet uses XML namespaces to distinguish between element types defined in XSLT and those defined elsewhere:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="Address">
<!-- The Addresses element type is not part of the XSLT namespace. -->
<Addresses>
<xsl:apply-templates/>
</Addresses>
</xsl:template>
</xsl:stylesheet>

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