Persistent Data - Research School of Computer Science€¦ · Persistent Data Danny (Yanming) Feng Adapted from previous lectures by Sid Chi-Kin Chau, Michael Curtotti and Eric McCreath.

Persistent Data

Danny (Yanming) FengAdapted from previous lectures by

Sid Chi-Kin Chau, Michael Curtotti and Eric McCreath

2

I. OverviewII. Bespoke and SerialisationIII. XML and JSON

ANU College of Engineering & Computer Science - COMP2100/6442


Goals

Explore XML and JSON as approaches to data persistence

Demonstrate the approaches by looking at simple implementations


XML Application example: .docx


XML Application example: .docx


XML Implementation Example Tree Structure Root Element Child Element Attribute <customer id=”123”

status=”active”>


Two major options for XML in Java Two approaches – DOM and SAX

SAX – Simple API for XML

DOM – Document Object Model (structured around XML standard)

SAX treats xml as stream and allows extraction of data as stream is read- preferable for very large documents (gigabyte)

SAX very fast and efficient as compared as DOM

Java DOM reads in entire XML tree and generate the node object


XML - DOM Root ElementCompany

ElementEmployee

ElementEmployee

AttributeNon-Technical

AttributeTechnical

ElementFirstNameElement

FirstNameElementPhone

ElementLastName

ElementFirstName

ElementPhone

ElementLastName

ElementFirstName

ElementPhone

TextSid

Text012345

TextSid

TextChau

Text543210

TextTom

TextJerry


Using DOM DOM requires a number of steps to save data to file: - DocumentBuilderFactory used to generate a DocumentBuilder - Document created from a DocumentBuilder object - Then a matter of creating appropriate elements and appending them in appropriate tree (e.g. gender element a child of person element – append text node as gender element) - Then further steps to get it ready for a output file Similar series of steps for DOM loading - DocumentBuilderFactory - Document Builder - Document - Class data structures


Advantages and Disadvantages+ Robust, Extensible+ Involved to implement+ Human readable+ Portable, Platform independent and programming language independent+ XML supports Unicode (international encoding) + Easy format verification- XML syntax is verbose and redundant- XML file sizes are usually big because of above- Doesn’t support Array


JSON JavaScript Object Notation (JSON), like XML, is also an

open standard format that is widely used.

Originally designed for sending data between web client and server, but also very useful for data storage.

Built around attribute-value pairs and produces smaller and more readable documents than XML.

JSON example: {“age”:21,”name”:”Marry”}


Advantages and Disadvantages+ More lightweight+ Straightforward to implement+ Support array and null+ can easily distinguish boolean, number, and string type

- Lacking language features of XML(e.g. xml attributes..)- Not native support in Java


JSON syntax and types {“attribute-name”:{JSON object}}

{“attribute-name”:”string”}

{“attribute-name”:[array]}

{“attribute-name”:1} (number)

{“attribute-name”:true} (boolean)

{“attribute-name”:null}


Example Exam QuestionsQ1: Describe the JSON format. Illustrate your description with a JSON document that could be used for storing a person's name, phone and address.

Q2: What are the advantages of storing persistent data using XML or JSON files rather than using Serializable Java Objects?

Q3: In the context of persistent storage which statement is correct?A. The kind of data we are using is irrelevant to our choice of data persistence.B. Bespoke methods often lack robustness.C. JSON uses the same tag syntax as XML for marking up data.D. JSON runs an SQL database to store data.

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Recommended Reading


- Kay Horstmann, Big Java (Chapters on XML)

- W3C XML standards pages https://www.w3.org/standards/

- JSON https://www.json.org/

- The JavaScript Object Notation (JSON) Data Interchange Format https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf

- 10 JSON Examples to Use in Your Projects https://www.sitepoint.com/10-example-json-files/

https://www.w3.org/standards/

https://www.json.org/

https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf

https://www.sitepoint.com/10-example-json-files/

All demo code will be on Git

If you have any question feel free to post it on the course forum

My email: [email protected]

Thank you!

mailto:[email protected]

Persistent Data - Research School of Computer Science€¦ · Persistent Data Danny (Yanming) Feng Adapted from previous lectures by Sid Chi-Kin Chau, Michael Curtotti and Eric McCreath.

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