Introduction to XML. Programming models Distributed programming models Typical Web-based Easy to...
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Distributed programming modelsDistributed programming modelsTypical Web-basedTypical Web-based
Easy to deploy but slow, not great user experienceEasy to deploy but slow, not great user experience
htmlbrowser
WebServer
http
DynamicallyGenerated
html
Many programming models•JSP•Servlets•PHP•CGI (python, perl, C)•Cold Fusion
html
plus optionallyJavaScript to jazz up html
database
Distributed programming modelsDistributed programming modelsTypical Web-basedTypical Web-based
Better user experience. Heavier, less portable, requires Better user experience. Heavier, less portable, requires socket programming to stream to server.socket programming to stream to server.
WebServer
http
DynamicallyGenerated
html
html + applet
databaseapplet
html
socket
Direct ConnectionsDirect Connections
Application client
App1sockets
App2
App3
ports
Application client
App1
Remote ProceduresApp2
App3N
DS
Examples: Java’s rmi, CORBA
XML Basics, contXML Basics, cont
Most modern languages have method of Most modern languages have method of representing structured data.representing structured data.
Typical flow of events in applicationTypical flow of events in application
Read data(file, db, socket)
Marshalobjects
Manipulate inprogram
Unmarshal (file, db, socket)
•Many language-specific technologies to reduce these steps: RMI, object serialization in any language, CORBA (actually somewhat language neutral), MPI, etc.
•XML provides a very appealing alternative that hits the sweet spot for many applications
User-defined types in programming User-defined types in programming languageslanguages
XML is a text-based, programming-language-XML is a text-based, programming-language-neutral way of representing structured neutral way of representing structured information. Compare:information. Compare:
struct Student{ char* name; char* ssn; int age; float gpa;}
class Student{ public String name; public String ssn; public int age; public float gpa;}
C Java Fortrantype Student character(len=*) :: name character(len=*) :: ssn integer :: age real :: gpaend type Student
Sample XML SchemaSample XML Schema
•In XML, datatype description is called a schema.
<?xml version="1.0" encoding="UTF-8"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified"> <xs:element name="student"> <xs:complexType> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="ssn" type="xs:string"/> <xs:element name="age" type="xs:integer"/> <xs:element name="gpa" type="xs:decimal"/> </xs:sequence> </xs:complexType> </xs:element></xs:schema>
Ignore thisFor now
Alternative schemaAlternative schema
In this example studentType is defined separately rather than anonymously
<xs:schema> <xs:element name="student" type="studentType“/> <xs:complexType name="studentType"> <xs:sequence>
<xs:element name="name" type="xs:string"/><xs:element name="ssn" type="xs:string"/><xs:element name="age" type="xs:integer"/><xs:element name="gpa" type="xs:decimal"/>
</xs:sequence> </xs:complexType></xs:schema>
new type defined separately
Alternative: DTDAlternative: DTD
Can also use a DTD (Document Type Descriptor), but this is probably becoming obsolete (notice the lack of types)
<!DOCTYPE Student [ <! – Each XML file is stored in a document whose name is the same as the root node -- > <! ELEMENT Student (name,ssn,age,gpa)> <! – Student has four attributes -- > <!ELEMENT name (#PCDATA)> <! – name is parsed character data -- > <!ELEMENT ssn (#PCDATA)> <!ELEMENT age (#PCDATA)> <!ELEMENT gpa (#PCDATA)>]>
Creating instances of typesCreating instances of types
In programming languages, we instantiate objects:
struct Student s1, s2;s1.name = “Andrew”s1.ssn=“123-45-6789”;
Student s = new Student();s1.name = “Andrew”;s1.ssn=“123-45-6789”;.type(Student) :: s1s1%name = ‘Andrew’.
C
Java
Fortran
Creating XML documentsCreating XML documents
XML is XML is notnot a programming language! a programming language!
In XML we make a Student “object” in an xml file In XML we make a Student “object” in an xml file (Student.xml):(Student.xml):
<Student><Student>
<name>Andrew</name><name>Andrew</name>
<ssn>123-45-6789</ssn><ssn>123-45-6789</ssn>
<age>36</age><age>36</age>
<gpa>2.0</gpa><gpa>2.0</gpa>
</Student> </Student>
Think of this as like a serialized object.Think of this as like a serialized object.
XML and SchemaXML and Schema
Note that there are two parts to what we didNote that there are two parts to what we did Defining the “structure” layoutDefining the “structure” layout Defining an “instance” of the structureDefining an “instance” of the structure
The first is done with an appropriate Schema The first is done with an appropriate Schema or DTD.or DTD.The second is the XML partThe second is the XML partBoth can go in the same file, or an XML file Both can go in the same file, or an XML file can refer to an external Schema or DTD can refer to an external Schema or DTD (typical)(typical)From this point on we use only SchemaFrom this point on we use only Schema
XMLSpyXMLSpy
Excellent tool for both Excellent tool for both learninglearning and and developing developing XML.XML.
Many XML books contain free 90-day license. Many XML books contain free 90-day license. Otherwise, free 30-day license on web page for Otherwise, free 30-day license on web page for professional and totally free home editionprofessional and totally free home edition
Try to use XMLSpy to create example just Try to use XMLSpy to create example just covered.covered.
Aspects of XML syntaxAspects of XML syntax
It is illegal to omit closing tagsIt is illegal to omit closing tags
XML tags are case-sensitiveXML tags are case-sensitive
XML elements must be properly nestedXML elements must be properly nested
XML elements must have a root elementXML elements must have a root element
XML preserves whitespacesXML preserves whitespaces
XML comments:XML comments:
< -- This is a comment -- >< -- This is a comment -- >
How is XML UsefulHow is XML Useful
Part IPart I
Simple Mortgage CalculatorSimple Mortgage Calculator
Mortgage payment calculatorMortgage payment calculator
Design a simple application which does the Design a simple application which does the following:following: Accepts user inputAccepts user input
Loan amountLoan amount
Loan termLoan term
Interest rateInterest rate
Extras (assessments + taxes)Extras (assessments + taxes) Returns per-month table ofReturns per-month table of
total paymenttotal payment
interestinterest
PrincipalPrincipal
Some other fun stuffSome other fun stuff
Mortgage Calculator General Mortgage Calculator General RequirementsRequirements
Must beMust be Clean simple interface (easy)Clean simple interface (easy) Remotely accessible with securityRemotely accessible with security PortablePortable Not require too much installation on the part Not require too much installation on the part
of the userof the user Sufficiently fast not to be embarrassingSufficiently fast not to be embarrassing
Some possible architecturesSome possible architectures
Web serverWeb server Server-side scripting with pure htmlServer-side scripting with pure html Server-side scripting with html+javascriptServer-side scripting with html+javascript Server-side scripting with html+appletServer-side scripting with html+applet
Direct connectionDirect connection Raw socketsRaw sockets Distributed objectsDistributed objects
Initial architectureInitial architecture
Front-end: pure html formFront-end: pure html form
Back end: python cgi (similar to java servlet)Back end: python cgi (similar to java servlet) Python generates web page dynamically after making Python generates web page dynamically after making
calculationscalculations No use of higher-level web generation libraries at this pointNo use of higher-level web generation libraries at this point
What are advantages/disadvantages of this architecture?What are advantages/disadvantages of this architecture?
Run application: Run application: http://masters.cs.uchicago.edu/~asiegel/courses/cspp53025/caseStudies/mortgagehttp://masters.cs.uchicago.edu/~asiegel/courses/cspp53025/caseStudies/mortgage
DisadvantagesDisadvantages
Two obvious disadvantages are:Two obvious disadvantages are: Formatted web content in print statements low-level, Formatted web content in print statements low-level,
ugly error proneugly error prone Data is not decoupled from formatting. What if we Data is not decoupled from formatting. What if we
want to switch to an application client?want to switch to an application client?
Several strategies can help with both of these Several strategies can help with both of these (higher-level htmlgen libraries, server-side (higher-level htmlgen libraries, server-side scripting model, beans, etc.) and XMLscripting model, beans, etc.) and XML
We will look at how XML fits in We will look at how XML fits in
XML-based architectureXML-based architecture
webbrowser
WebServer
http
“hand-rolled”XML
XML
pyth
on C
GI
“hand-rolled”XML
File system
Observations/questionsObservations/questions
What does browser do with XML?What does browser do with XML? Can it displayCan it display Does it even understand XML?Does it even understand XML?
If not, what good is this?If not, what good is this?
Do we have to hand roll our programming Do we have to hand roll our programming language objects from XML?language objects from XML?
Some answersSome answers
Regarding first point, try this with your web Regarding first point, try this with your web browserbrowser Note that XML is displayed/formatted nicely, but not Note that XML is displayed/formatted nicely, but not
nearly to the same level of utility as the html tablenearly to the same level of utility as the html table To add formatting instructions, we must associate a To add formatting instructions, we must associate a
separate separate XSLXSL file with the XML file. We will study XSL file with the XML file. We will study XSL soon.soon.
Regarding XML-language conversion, we will Regarding XML-language conversion, we will study language binding for various high-level study language binding for various high-level ways of doing this! For now, we will hand-roll ways of doing this! For now, we will hand-roll ourselves!ourselves!
XSLXSL
We will not cover details of XSL until the We will not cover details of XSL until the third week.third week.
However, for now we can easily create However, for now we can easily create XSL at a high level using XMLSpyXSL at a high level using XMLSpy
See example applicationSee example application
Lottery overviewLottery overview
Given a list of student members of a Given a list of student members of a dormitory, perform an ordered randomized dormitory, perform an ordered randomized sort of the students to determine a room sort of the students to determine a room draft order.draft order.
Lottery detailsLottery details
Students are defined byStudents are defined by Last nameLast name First nameFirst name SenioritySeniority
Quarters in the HouseQuarters in the HouseQuarters in the CollegeQuarters in the College
The sort keys areThe sort keys are1.1. Quarters in HouseQuarters in House2.2. Quarters in CollegeQuarters in College3.3. RandomRandom
Software requirementsSoftware requirements
Secure loginSecure login House nameHouse name PasswordPassword
Remotely accessibleRemotely accessible
Prototypes:Prototypes: Standalone Standalone excelexcel Web-basedWeb-based
Architectural requirementsArchitectural requirements
XMLLoginInfo
XMLStudent
Data
filesystem
WebServer
login
lottery
WebClient
XML
XSL
Next StepNext Step
Implement Lottery as specifiedImplement Lottery as specified
You must have the following:You must have the following: Student SchemaStudent Schema Password SchemaPassword Schema Sample student xmlSample student xml Sample password xmlSample password xml Simple XSL for displaySimple XSL for display