3/6 - XML

Question 1

What does XML stand for?

Answer 1

eXtensible Markup Language

Question 2

What does XML do?

Answer 2

• Use to add lightweight semantic info (what the code means) to plain text
• It can describe complex structured data
• It is not a programming language, it’s just data

Question 3

What does DTD stand for?

Answer 3

Document Type Definition

Question 4

What is DTD?

Answer 4

• Just a general structure for a family of XML documents
• We can have one DTD (specifies the grammar/syntax) and have many XML document that obey that DTD
• This is similar to having one HTML syntax and many HTML pages that obey that syntax

Question 5

XPath

Answer 5

• Compact syntax for grabbing fragments of XML data
• Vaguely similar to regular expressions
• It is a way of picking out a piece of an XML document

Question 6

What does XSLT stand for?

Answer 6

eXtensible Stylesheet Language Transformation

Question 7

What is XSLT?

Answer 7

• It is similar to a programming language, since it has conditionals, loops etc
• It is a language for transforming XML
• Uses XPath

Question 8

What are Markup Languages?

Answer 8

• Markup languages give structure and meaning to plain text
• The idea behind markup languages is to add some semantic info (meaning or structure) to plain text
• They are like a lightweight overlay on top of your plain text

Question 9

Creating Your Own Markup Language

Answer 9

• HTML is one of the markup language. It is used for describing web pages
• If web pages are not the things you are interested in, then you can make your own markup vocabulary.
• XML provides a generic syntax for defining your own custom markup language

Question 10

XML start and end tags

Answer 10

angle brackets (e.g. basil )

Question 11

XML how to delimit elements

Answer 11

• Tags delimit elements.

* The whole thing from the start tag (<>) to the end tag (>) defines an element

Question 12

Where are XML attributes placed, and are they required?

Answer 12

Start tags have attributes which are optional. Duplicate attribute name is not allowed.

Question 13

XML shorter syntax for empty elements

Answer 13

e.g.

Question 14

XML element and attribute name

Answer 14

We can make up any element and attribute name

Question 15

How to use XML special characters?

Answer 15

Special characters cannot be used in XML unless you escape them
• “” has to be used as &gt
• “&” has to be used as &amp
• Characters not in ASCII have to be used by their Unicode representation

Question 16

Nesting XML elements

Answer 16

Elements must be strictly nested and explicitly closed

Think of elements as nested matching parentheses.

Question 17

root element

Answer 17

the top level element (there is exactly ONE)

Question 18

XML docs as trees

Answer 18

Every well-formed XML document is a tree

Strict nesting determines parent child relationship

Question 19

What are the nodes in the tree?

Answer 19

Elements are nodes

• May have zero or more ordered children

Question 20

What are the leaf nodes?

Answer 20

Runs of original text become leaf nodes (they cannot have any children)

Question 21

What purpose do attributes serve, in the context of a tree?

Answer 21

Attributes are extra info on elements

• Collection of key value pairs like {name: value}

Question 22

Are attributes ordered?

Answer 22

Attributes are unordered unlike child nodes

Question 23

Extra parsing of attribute values

Answer 23

No extra parsing or interpretation of attribute values

Question 24

Well Formed XML

Answer 24

Requires only proper syntax, nesting, entity escaping
• Sufficient to ensure that one can construct an unambiguous tree
• Every XML parser will interpret your XML in the same way
• XML is used to exchange data between different computers, so every parser must have a consistent interpretation.
• If XML is not well formed then it is not XML

Question 25

Validated XML

Answer 25

• Must be at least well-formed XML
• Document tree obeys extra rules about, what appears where
• Rules provided by designer of markup vocabulary

Question 26

DTD: Document Type Definition

Answer 26

• Gives the general format of a family of XML documents
  
  • Gives a set of rules that describe what is allowed where
• If an XML doc is not well formed parser cannot even try to validate it.
• Many parsers offer both validating and non validating modes

Question 27

Validating vs Non-Validating XML parser

Answer 27

• A validating XML parser first constructs the tree to make sure your document is well formed and then it checks it against the DTD.
• A non-validating parser only checks for well formed XML

Question 28

DTD Element Properties

Answer 28

1. Ordering
2. Repetition
3. Special kinds of content

Question 29

Ordering

Answer 29

• Ordering of child nodes, if any are allowed
• Specific order: foo, bar, baz
• Mixed in any order: foo, bar, baz

Question 30

Repetition

Answer 30

?: Zero or one repetition. Means that it is optional. Example: foo?

: Zero or more repetition. Example: bar

+: One or more repetition. Example: baz+

Question 31

Special kinds of content

Answer 31

• EMPTY. Element must have nothing. It is not even allowed to be wrapped around text
• # PCDATA : Just means plain text. Stands for Parsed Character DATA. Not allowed to have any elements in it. So if you have any > or < you must escape them using &

Question 32

Example: General Shakespearean Play in DTD

Answer 32

: title is just wrapped around parsed character

Question 33

Disclaimer about DTD and XML

Answer 33

A DTD itself is NOT an XML document. They are defined by SGML.

DTDs use < or >. They are not XML. DTD describes the grammar of XML doc

Question 34

DTD Attribute Properties

Answer 34

Each element has a list of allowed attributes

Each attribute has a NAME, TYPE and DEFAULT VALUE