1. COMP9321 Web Application Engineering Semester 2, 2017
Dr. Amin Beheshti
Service Oriented Computing Group, CSE, UNSW Australia
Week 11
(Wrap-up)
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2. Assignments
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3. Assignments Assignment 1 – GradeBook Assignment 2 – GradeBook
Assignment 3 – Due end of Week 12
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4. Final Exam
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5. Final Exam
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6. Final Exam
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7. Final Exam
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8. Sample Final Exam
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9. COMP9321, 17s2, Week11

10. Must illustrate your answer with an example.
Sample Question:
Why is the stateless nature of HTTP a problem in Web application development? You
Must illustrate your answer with an example.
COMP9321, 17s2, Week11

11. Must illustrate your answer with an example.
Sample Question:
Why is the stateless nature of HTTP a problem in Web application development? You
Must illustrate your answer with an example.
COMP9321, 17s2, Week11

12. Sample Question:
Describe the Model-View-Controller (MVC) architecture pattern in detail. What are
the advantages of using MVC over an architecture based solely on JSP pages?
COMP9321, 17s2, Week11

13. Sample Question:
Describe the Model-View-Controller (MVC) architecture pattern in detail. What are
the advantages of using MVC over an architecture based solely on JSP pages?
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14. Week 1 – 11 Review
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15. Different Layers in an Application
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16. Presentation Layer HTML <form> method attribute specifies
how to send form-data  as
URL variables (with method="get") , or
HTTP post transaction (with method="post").
Method? Get/Post
COMP9321, 17s2, review>Week 2

17. Static vs. Dynamic Web Page
A static web page is delivered to the user exactly as stored, in contrast to dynamic web pages which are generated by a web application, and on demand!
is-a
web page whose construction is controlled by an application server processing server-side scripts.
is-a
e.g.
software framework that provides both facilities to create web applications and a server environment to run them.
Java application servers
It's core set of API and features are defined by Java EE.
The Web modules include Java Servlets and Java Server Pages.
COMP9321, 17s2, review>Week 2

18. Java Servlets http://java.sun.com/products/servlet/index.jsp
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19. A Lifecycle of a Servlet
The Web container controls the lifecycle of a servlet class:
initialisation
ServletConfig
ServletContext …
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20. Attributes and Sharing Attributes
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21. Managing the User State
A problem in HTTP request/response:
HTTP is a stateless protocol.
A single request/response;
Nothing is remembered 'between requests' from the same user;
Web applications need to maintain users + their data.
It is a programmer's responsibility:
The term "session" is used to represent the data associated with one user while she navigates around a Web application.
Session is a conversional state between client and server.
Session can consists of multiple request and response between client and server.
Since HTTP is stateless, the only way to maintain a session is when some unique information about the session (session id) is passed between server and client in every request and response.
COMP9321, 17s2, review>Week2

22. Cookies
Cookies are text files stored on the client computer and they are kept for various information tracking purpose.
Java Servlets transparently supports HTTP cookies.
There are three steps involved in identifying returning users:
Server script sends a set of cookies to the browser. e.g. session id
Browser stores this information on local machine for future use.
Next time, browser sends request + those cookies to the server and server uses that information to identify the user.
COMP9321, 17s2, review>Week2

23. JavaServer Pages (JSP) Technology
JavaServer Pages (JSP) technology allows you to easily create web content that has both static and dynamic components.
JSP technology makes available all the dynamic capabilities of Java Servlet technology; but provides a more natural approach to creating static content.
JSP is similar to PHP, but it uses the Java programming language.
To deploy and run JavaServer Pages, a compatible web server with a servlet container, such as Apache Tomcat, is required.
COMP9321, 17s2, review>Week3

24. JSP
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25. JSP Basics Scriptlet Expression Declaration Comments Traditional
Scripting
Elements
EL Scripting
${…}
Modern
JSP Elements
Page
Include
Taglib
Directive
Elements
JSP Page
custom
<abc:mytag>
Action
Elements
<jsp:useBean>
<jsp:getProperty>
<jsp:setProperty>
<jsp:include>
<jsp:forward>
<jsp:param>
Standard
Template Text (HTML bits…)
COMP9321, 17s2, review>Week3

26. Extensible Markup Language (XML)
XML originally designed to meet the challenges of large-scale electronic publishing.
XML separates presentation issues from the actual data.
XML plays an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere.
Needs a communication protocol?
e.g. SOAP stands for Simple Object Access Protocol
SOAP is based on XML
SOAP is a W3C recommendation
SOAP uses XML Information Set for its message format.
COMP9321, 17s2, review>Week4

27. The XML Family XML: a markup language used to describe information.
DOM: a programming interface for accessing and updating documents.
DTD and XML Schema: describes the structure and content of XML documents.
XSLT: a language for transforming XML documents
XPath: a query language for navigating XML documents.
XPointer: for identifying fragments of a document.
XLink: generalises the concept of a hypertext link.
XInclude: for merging documents.
XQuery: a language for making queries across documents.
RDF: a language for describing resources.
COMP9321, 17s2, review>Week4

28. Semantic Web
It is a collection of standard technologies to realize a Web of Data!
RDF, OWL, SPARQL, etc.
Web of Data beyond the Web of Documents!
Machine Readable
Human Readable
The amount of information is growing exponentially. 
COMP9321, 17s2, review>Week5

29. W3C's "Semantic Web Vision“
Web information has exact meaning
Web information can be understood and processed by computers
Computers can integrate information from the web
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30. Resource Description Framework (RDF)
RDF is a framework for describing resources on the web.
Publishing such descriptions on the Web creates the Semantic Web.
RDF uses Web identifiers (URIs) to identify resources.
e.g.
Web documents
concepts from the real world (e.g. people, organisations, topics, things)
URIs (Uniform Resource Identifiers) are very important, providing both the core of the framework itself and the link between RDF and the Web.
COMP9321, 17s2, review>Week5

31. Web Ontology Language (OWL)
Ontology is about the exact description of things (web information) and their relationships.
OWL was designed to provide a common way to process the content of web information
OWL and RDF are much of the same thing, but OWL is a stronger language with greater machine interpretability than RDF.
OWL provides additional vocabulary along with a formal semantics
OWL making it easier for machines to automatically process and integrate information available on the Web.
OWL has three sublanguages
OWL Lite
OWL DL
OWL Full
OWL is complex:
OWL is a large set of additional terms
COMP9321, 17s2, review>Week5

32. Rules There is a long history of rule languages and rule-based systems
eg: logic programming (Prolog), production rules
Lots of small and large rule systems
E.g. from mail filters to expert systems
Why rules on the Semantic Web?
There are conditions that ontologies (ie, OWL) cannot express
a well known example is Horn rules: (P1 ∧ P2 ∧ …) → C
COMP9321, 17s2, review>Week5

33. A new requirement: exchange of rules
Applications may want to exchange their rules:
e.g. negotiate eBusiness contracts across platforms
e.g. describe privacy requirements and policies
Rule Interchange Format (RIF):
Goals:
expresses the rules a bit like a rule language
can be used to exchange rules among engines
Challenges:
Rule based systems can be very different
different rule semantics
A universal exchange format is not feasible
COMP9321, 17s2, review>Week5

34. Linking Open Data (LOD)
- Goal: “expose” open datasets in RDF
- Set RDF links among the data items from different datasets
- Set up query endpoints
- Result: billions of triples and millions of links…
- The important point here is that :
the data becomes available to the World via a unified format (ie, RDF).
the various datasets are interlinked together
e.g. DBpedia project
COMP9321, 17s2, review>Week5

35. Query RDF Data (SPARQL)
SPARQL Protocol And RDF Query Language, is an RDF query language.
This specification defines the syntax and semantics of the SPARQL query language for RDF.
SPARQL can be used to express queries across diverse data sources.
SPARQL contains capabilities for querying required and optional graph patterns
The results of SPARQL queries can be results sets or RDF graphs.
COMP9321, 17s2, review>Week5

36. Data Persistence
When you work with a relational database in a Java application, the Java code issues SQL statements to the database via the JDBC API.
The Java Database Connectivity (JDBC) API provides universal data access from the Java programming language.
Using the JDBC API, you can access virtually any data source, from relational databases to spreadsheets and flat files. 
The JDBC API is comprised of two packages:
java.sql
javax.sql
(Hibernate, pp.5-29)
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37. Accessing DB from an Application
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38. PreparedStatement object
A more realistic case is that the same kind of SQL statement is processed over and over (rather than a static SQL statement).
In PreparedStatement, a place holder (?) will be bound to an incoming value before execution (no recompilation).
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39. Data Access Objects (DAO)
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40. Object-Relational Impedance Mismatch Problems
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41. Object-Relational Impedance Mismatch Problems
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42. What is NoSQL? Stands for No-SQL or Not Only SQL??
Class of non-relational data storage systems
E.g. BigTable, Dynamo, PNUTS/Sherpa, ..
Usually do not require a fixed table schema nor do they use the concept of joins
Distributed data storage systems
All NoSQL offerings relax one or more of the ACID properties (will talk about the CAP theorem)
Chapter 19: Distributed Databases
COMP9321, 17s2, review>Week6

43. CAP Theorem Three properties of a system
Consistency (all copies have same value)
Availability (system can run even if parts have failed) Via replication.
Partitions (network can break into two or more parts, each with active systems that can’t talk to other parts)
Brewer’s CAP “Theorem”: You can have at most two of these three properties for any system.
Very large systems will partition at some point.
COMP9321, 17s2, review>Week6

44. Design Patterns
A pattern is a proven solution to a problem in a context.
Each pattern expresses a relation between a certain context, a problem, and a solution.
A design pattern represents a solutions to problems that arise when developing a software.
Frameworks
Subsystems
Sub-subsystems
Design pattern are granular and applied at different levels such as:
Design
Architectural
Analysis
Creational
Structural
Behavioral
Categories include:
COMP9321, 17s2, review>Week7

45. J2EE Design Patterns
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46. General Guideline for Servlet/JSP/JavaBeans
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47. Securing your Web Application: Threats!
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48. Securing your Web Application: Threats!
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49. Session Management…
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50. Transport Layer Security (e.g. HTTPS)
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51. Performance
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52. Performance Metrics Response Time Throughput Availability Reliability
Resource Utilization
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53. Scalability
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54. Operational Laws Utilization Law Little’s Law Forced Flow Law
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55. Architectural Considerations - Network
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56. General Techniques for Improving Performance and Scalability
Caching/Replication
Parallelism
Redundancy
Asynchrony
Resource Pooling
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57. Improving Performance using HTTP features
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58. Improving Database Access
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59. Some Updates from s1-2018 COMP9321: Data Services Programming
This course aims to introduce the student to core concepts and practical skills for engineering the data in service-oriented data-driven applications.
COMP9322: Software Service Design Engineering
This course arms students with the knowledge and expertise to “design” and “engineer” services using modern Web technology.
COMP9323: SaaS Project
This course aims to practice what you have learned in COMP9321 and COMP9322 courses by getting involved in implementing real-world projects.
COMP6324: Internet of Things Service Design and Engineering
This course focuses on the engineering and management aspects of IoT Services, providing complementary skills and knowledge to what is offered by existing courses.
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60. Next Week Q&A: Assignment Implementation/Report
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61. Next: Open Lecture Big Data: Challenges and Opportunities
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62. Good Luck!
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63. COMP9321, 17s2, Week11