XML Introduction

Question 1

Fully Structured Data

Answer 1

This is where data in a relational model is structured and has to fit a schema, like Module(code, name).

Question 2

Unstructured Data

Answer 2

Things like music and image files, where it is completely free on how to organise data.

Question 3

Semi-structured Data

Answer 3

This contains no schema, and it flexible, but is also self-describing in a way.

Question 4

Semi-structured Data model

Answer 4

A data model for the semi-structured data may be thought as a collection of nodes and edges in a tree-like manner.

Question 5

Applications for semi-structured data

Answer 5

• Storing and sharing data on the web
• Storage of documents
• Data analytics and big data

Question 6

Forms of semi-structured data

Answer 6

• XML
• JSON
• Simple key-value relationships
• Graphs

Question 7

XML

Answer 7

XML files have a very similar structure to HTML files, where you have items in backets, <>, which descend to represent lower details in the tree.

Question 8

XML Elements

Answer 8

Anything that is contained within an elements start tag and end tag, and can contain text, attributes and/or other elements.

<price>1.99</1.99>
</price>

Question 9

Element Parents

Answer 9

Since we work in a top-down structure, we can nest elements within each other to declare hierarchy.

<person>
<student>
</student>
</person>

Question 10

Attributes

Answer 10

Things that help define elements.
<person hair=”blonde”
</person
They can be very helpful in defining references.

Question 11

Two ways of defining XML file format

Answer 11

DTD and XML Schema.

Question 12

DTD

Answer 12

Document type definitions.
Provided information about the structure of the document.

Question 13

DTD includes

Answer 13

• elements
• sub-elements
• attributes

Question 14

<!DOCTYPE lecturers [

]>

Answer 14

Beginning of XML document.
Lecturers is the root name.

Question 15

<!ELEMENT lecturers (lecturer+)>

Answer 15

+ means that there must be one or more lecturer in lecturer.

Question 16

<!ELEMENT lecturer (name, phone?, email?, teaches*)>

Answer 16

Name is required, but we don’t have permission for multiple unlike using +.
Phone and email are optional, and can either have ONE or none.
Teachers can either have none, or many. So the lecturer could teach nothing, one lesson or multiple lessons.

Question 17

DTD Format

Answer 17

When defining elements with child nodes in DTD, they have to be stated later on.
For example:
<!ELEMENT lecturer (name, phone, email)>
Since this element has name, phone and email, they need to be defined later in the document like this:
<!ELEMENT lecturer (name, phone, email)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
<!ELEMENT email (#PCDATA)>

Question 18

PCDATA

Answer 18

Special symbol for text data.

Question 19

Defining attributes in DTD

Answer 19

Lets say you have, in XML:
<student name=”Jake” year=2
In DTD, we represent this differently:
<!ELEMENT student EMPTY>
<!ATTLIST student name CDATA #IMPLIED>
<!ATTLIST student year CDATA #REQUIRED>

Question 20

ATTLIST

Answer 20

Simply enough, attribute list.

Question 21

IMPLIED

Answer 21

Means optional.

Question 22

REQUIRED

Answer 22

Means required.

Question 23

FIXED

Answer 23

Means a constant.

Question 24

CDATA

Answer 24

Character data, containing any text.

Question 25

ID

Answer 25

Used to identify individual elements in documents.

Question 26

IDREF/IDREFS

Answer 26

Must correspond to value of ID attributes for some element in document.
Essentially allows a unique key to identify multiple elements.

Question 27

ID example

Answer 27

<lecturer>
<!ATTLIST lecturer staffNo ID #required>
</lecturer>

Question 28

Two levels of document processing

Answer 28

• well-formed
• valid

Question 29

DTD Document Processing
Validating/non-validating processors

Answer 29

Non-validating processor ensures XML document is well-formed before passing information onto application.
Validating processor will not only check for well-formedness, but also if it conforms to a DTD, which results in it being valid.