web programming week 2
DESCRIPTION
Web Programming Week 2. Old Dominion University Department of Computer Science CS 418/518 Fall 2010 Martin Klein 09/07/10. Defining the Web / HTTP. HTTP was originally defined by Request for Comments (RFCs)1945, 2068, 2616 - PowerPoint PPT PresentationTRANSCRIPT
Web Programming
Week 2
Old Dominion UniversityDepartment of Computer Science
CS 418/518 Fall 2010
Martin Klein <[email protected]>
09/07/10
Defining the Web / HTTP• HTTP was originally defined by Request for
Comments (RFCs)1945, 2068, 2616– and several others for defining URLs, URIs, etc.
• While RFC 2616 remains canonical for HTTP, we have a new document for the “Web” (URIs + protocols + formats), we have a slightly revisionist but ultimately useful unifying document:– The Architecture of the World Wide Web, Volume
One.• http://www.w3.org/TR/webarch/
How To Read RFCs
(quoting from RFC 2119)
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
1. MUST This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification.
2. MUST NOT This phrase, or the phrase "SHALL NOT", mean that the definition is an absolute prohibition of the specification.
3. SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.
4. SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label.
5. MAY This word, or the adjective "OPTIONAL", mean that an item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product while another vendor may omit the same item. An implementation which does not include a particular option MUST be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality. In the same vein an implementation which does include a particular option MUST be prepared to interoperate with another implementation which does not include the option (except, of course, for the feature the option provides.)
Examples from RFC 261610.4.6
405 Method Not Allowed
The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.
10.4.4
403 Forbidden
The server understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated.
10.4.9
408 Request Timeout
The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.
Reading the W3C Arch
• Principles– fundamental “rule” or “law” that is widely applicable
• Constraints– definitions imposed by the architects of the Web– “MUST”, “SHALL”
• Good Practice– things you should be doing, but they can’t / shouldn’t
be defined as constraints – “SHOULD”, “RECOMMENDED”
Principle: Global Identifiers
• Principle: Global Identifiers– Global naming leads to global network effects.
Good practice: Identify with URIs
• Good practice: Identify with URIs– To benefit from and increase the value of the
World Wide Web, agents should provide URIs as identifiers for resources.
Constraint: URIs Identify a Single Resource
• Constraint: URIs Identify a Single Resource– Assign distinct URIs to distinct resources.
Uniform Resource Identifiers
URI
URL URN
RFC 3986 (2396)
RFC 2141RFC 1738
URI Schemes
foo://username:[email protected]:8042/over/there/index.dtb;type=animal?name=ferret#nose \ / \________________/\_________/ \__/ \___/ \_/ \_________/ \_________/ \__/ | | | | | | | | | | userinfo hostname port | | parameter query fragment | \_______________________________/ \_____________|____|____________/scheme | | | | | authority |path| | | | | path interpretable as filename | ___________|____________ | / \ / \ | urn:example:animal:ferret:nose interpretable as extension
taken from: http://en.wikipedia.org/wiki/URI_scheme
remember: • URIs identify Resources• Representations represent Resources• When URIs are dereferenced, they return representations (i.e., a resource is never returned)
taken from: http://www.w3.org/TR/webarch/
Important Web Architecture Concepts (As defined by the Web Architecture)
W3C Web Architecture
Resource
URIRepresentation 2
Represents
Representation 1
Represents
Identifies
Content Negotiation
The tools we have to solve the interoperability problem are:
• Resource• URI• Representation
slide from Herbert Van de Sompel
LAMP
• Chapters 3, 10 of textbook– more info: http://dev.mysql.com/doc/
• Quick review of relational databases– normalization– referential integrity
• Basic MySQL commands
“Graphic Novel” Super Heroes (from chapter 10)
name real name
power 1 power 2 power 3 lair address
city state zip
Clean Freak
John Smith
Strength X-ray vision
flight 123 Poplar Ave
Townsburg OH 45293
Soap Stud Efram Jones
Speed 123 Poplar Ave
Townsburg OH 45293
The Dustmite
Dustin Huff
Strength Dirtiness Laser Vision
452 Elm St. #3D
Burgtown OH 45201
What if we need to add a super hero with more than 3 powers?
1st Normal Form
• Eliminate repeating columns
• Add primary key to table– Unique– Must not change
• Maintain “atomicity“– Each cell is atomic, has only one item of data
1NF• add primary key to tables
• eliminate repeating columns
• each attribute is atomic
id name realname
power lairaddress
city state zip
1 CleanFreak
JohnSmith
Strength 123PoplarAve
Townsburg OH 45293
1 CleanFreak
JohnSmith
X-rayvision
123PoplarAve
Townsburg OH 45293
1 CleanFreak
JohnSmith
flight 123PoplarAve
Townsburg OH 45293
2 SoapStud
EframJones
Speed 123PoplarAve
Townsburg OH 45293
3 TheDustmite
DustinHuff
Strength 452Elm St.#3D
Burgtown OH 45201
3 TheDustmite
DustinHuff
Dirtiness 452Elm St.#3D
Burgtown OH 45201
3 TheDustmite
DustinHuff
LaserVision
452Elm St.#3D
Burgtown OH 45201
What if John Smith changes his name?
2nd Normal Form
• Honor 1st Normal Form
• Create separate tables for data duplicated across rows
• Be aware of relationships!– 1:1– 1:m– m:n
2NF• satisfy 1NF
• create separate tables for data duplicated across rows
id power1 Strength2 X-Ray
vision3 Flight4 Speed5 Dirtiness6 Laser
Vision
id lair_id name realname
align
1 1 CleanFreak
JohnSmith
good
2 1 SoapStud
EframJones
good
3 2 TheDustmite
DustinHuff
evil
id lairaddress
city state zip
1 123 PoplarAve
Townsburg OH 45293
2 452 ElmSt. #3D
Burgtown OH 45201
char_id power_id1 11 21 32 43 13 53 6
Are “city“ and “state“ directly related to the lairs?
3rd Normal Form
• Honor 1st & 2nd Normal Form
• Create separate tables for any transitive or partial dependencies
3NF• satisfy 2NF
• create separate tables for any transitive or partial dependencies
id power1 Strength2 X-Ray
vision3 Flight4 Speed5 Dirtiness6 Laser
Vision
id lair_id name realname
align
1 1 CleanFreak
JohnSmith
good
2 1 SoapStud
EframJones
good
3 2 TheDustmite
DustinHuff
evil
id zip_id lairaddress
1 45293 123 PoplarAve
2 45201 452 ElmSt. #3D
id city state45293 Townsburg OH45201 Burgtown OH
char_id power_id1 11 21 32 43 13 53 6
see note on p. 283 on why good/evil is not in a separate table
That’s About as Far As We’ll Go
• Other normal forms are possible (BCNF, 4NF, 5NF)– take a database class if you’re interested
• Referential integrity– a foreign key (“link”) into another table is no
longer valid– “404 Errors” are bad in databases and should
not happen• how bad is a function of the data itself…
MySQL Hierarchy
server=mln-web.cs.odu.edu
database=tennisplayers
table 1 table 2
table 3
database=superheroes
table 1 table 2
table 3
Manipulating Tables & Databases
• CREATE - create new databases, tables• ALTER - modify existing tables• DELETE - erase data from tables• DESCRIBE - show structure of tables• INSERT INTO tablename VALUES - put data in
table• UPDATE - modify data in tables• DROP - destroys table or database (values +
structure)more: http://dev.mysql.com/doc/refman/5.0/en/sql-syntax.html
Native MySQL Data Types
• Unlike Perl, PHP and other civilized languages, MySQL is big into data types:– http://dev.mysql.com/doc/refman/5.0/en/data-
types.html– many examples in chapter 3, 10
SQL Query Form
SELECT [fieldnames]FROM [tablenames]WHERE [criteria]ORDER BY [fieldname to sort on] [DESC]LIMIT [offset, maxrows]
more: http://dev.mysql.com/doc/refman/5.0/en/select.htmllook at chapters 3 and 10 for code examples