21/10/2011 1 Introduc.on to Databases G6921 and G6931 Web Technologies Dr. Séamus Lawless • Course Structure – 1) Intro to the Web – 2) HTML – 3) HTML and CSS – Essay Informa.on Session – 4) Intro to Databases – 5) Intro to Databases – 6) PHP and MySQL – 7) Reading Week – 8) PHP and MySQL – 9) PHP and XML – 10) CMS – 11) Analy.cs – 12) Visualisa.on • Course Structure – 1) Intro to the Web – 2) HTML – 3) HTML and CSS – 4) Intro to Databases – 5) Intro to Databases – 6) PHP and MySQL – 7) Reading Week – 8) PHP and MySQL – 9) PHP and XML – 10) CMS – 11) Analy.cs – 12) Visualisa.on • Course Structure – 1) Intro to the Web – 2) HTML – 3) HTML and CSS – Essay Informa.on Session – 4) Intro to Databases – 5) Intro to Databases – 6) PHP and MySQL – 7) Reading Week – 8) PHP and MySQL – 9) PHP and XML – 10) CMS – 11) Analy.cs – 12) Visualisa.on Housekeeping
Transcript
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Introduc.on to Databases
G6921 and G6931 Web Technologies Dr. Séamus Lawless
• Course Structure – 1) Intro to the Web – 2) HTML – 3) HTML and CSS – Essay Informa.on Session – 4) Intro to Databases – 5) Intro to Databases – 6) PHP and MySQL – 7) Reading Week – 8) PHP and MySQL – 9) PHP and XML – 10) CMS – 11) Analy.cs – 12) Visualisa.on
• Course Structure – 1) Intro to the Web – 2) HTML – 3) HTML and CSS – 4) Intro to Databases – 5) Intro to Databases – 6) PHP and MySQL – 7) Reading Week – 8) PHP and MySQL – 9) PHP and XML – 10) CMS – 11) Analy.cs – 12) Visualisa.on
• Course Structure – 1) Intro to the Web – 2) HTML – 3) HTML and CSS – Essay Informa.on Session – 4) Intro to Databases – 5) Intro to Databases – 6) PHP and MySQL – 7) Reading Week – 8) PHP and MySQL – 9) PHP and XML – 10) CMS – 11) Analy.cs – 12) Visualisa.on
Housekeeping
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Housekeeping
• You all have a Laptop? • Can you all get connected to the Internet? • Can you all get connected to your webspace through SHH?
• Can you use a URL to view your files? • Assessment – Con.nuous Assessment • Upload the files you create!
Retrieving Web Pages
• Every page has a unique uniform resource locator (URL)
• Web pages are stored on web servers that use HTTP to exchange informa.on with client soaware
• e.g.,
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Retrieving Web Pages
• Client program (browser) uses the local machine to connect to a domain name system (DNS) server
• DNS server translates the hostname into an internet protocol (IP) address
• Browser then aeempts to connect to server host using specific port
• Aaer connec.on, browser sends a HTTP request to the web server to request a page – usually a GET request
Exercise 1
• Use the HTML file from last week’s Exercise 4 • Add a Background Colour to the whole page • Using an inline style to do this
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Exercise 2
• Take the HTML file from the previous exercise • Change the background colour of each sec.on of the page
• Using an internal style sheet to do this
Exercise 3
• Take the HTML file from the previous exercise • Change the font, font colour and font size in each sec.on of the page
• Use an external style sheet to do this
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What is Data? • Data is any informa.on that you want to store and refer to again. Data can be: – Text – Numbers – Dates – Images – Videos – Files – Any other types of informa.on.
• For example, if you sell cakes, you can store the names, pictures, and recipes of your cakes, the prices and quan..es of boxes and the dates of sales…..
What is a Database?
• An organised collec.on of Informa.on, or Data…
• Organised to: – model aspects of reality – in a way that supports processes that require this informa.on • A collec.on of Manuscripts in an archive • Finding manuscripts by a specific author and where those manuscripts are located
– mostly, to make the data more useful!
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Advantages • Search and Retrieval – Filtered according to specific needs
• Reduced Data Redundancy – Ease of Update
• Greater Data Integrity • Independence from Applica.ons, Concurrent Access
• Improved Data Security • Reduced Costs for Data Entry, Storage and Retrieval
Databases
• There are many Database Models – Oaen referred to as “Data Models”
• The four most common are: – Hierarchical – Network – Rela.onal • Object Rela.onal
– Graph
ST3001 – MySQL Tutorial 1 -‐ University of Dublin, Trinity
College
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Hierarchical Database
• One of the oldest database models – Commonly used in Mainframe compu.ng
• Organised hierarchically with parent and child nodes (like a family tree!)
Network Database
• Also have a hierarchical structure • Uses “members” and “owners” rather than “parents” and “children”.
• Each member can have more than one owner
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Rela.onal Database
• Differs from previous models as it is not Hierarchical, but Rela.onal
• More flexible than either the hierarchical or network database models.
• Graph databases treat the rela.onship between things as equally important to the things themselves.
En.ty Rela.onship Diagrams
• An abstract and conceptual representa.on of informa.on
• Used to produce a “Conceptual Schema” of a Database – In simpler terms, it is used to iden.fy the requirements for, and support the design of a database
• Describes the type of informa.on that is to be stored in the database
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En..es, Rela.onships and Aeributes
• “An en4ty is a business object that represents a group, or category of data.” – Do we know a similar concept? – Each en.ty represents a table in the database
• “A rela4onship captures how two or more en..es are related to one another.”
• “An a6ribute is a sub-‐group of informa.on within an en.ty.” – Do we know a similar concept? – Each aeribute represents a column in a the table
• Provides a short descrip.on of the nature of the rela.onship
• It is always read clockwise with respect to the en..es that it links
Mandatory Rela.onships
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Op.onal Rela.onships
Mixed Par.cipa.on
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One to One
Many to Many
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One to Many
Recursive
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Many-‐to-‐Many Rela.onships
• Many-‐to-‐many rela.onships are difficult to encode in a rela.onal database
• They should be avoided where possible. • We can resolve a many-‐to-‐many rela.onship by: – Dividing it into two one-‐to-‐many rela.onships. – Using a linking table
Many-‐to-‐Many Rela.onships
• Think of the following example:
• Try to represent this using two tables and their aeributes
• We have a problem
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Many-‐to-‐Many Rela.onships
• We need a linking table:
• These types of rela.onships must be broken into mul.ple one-‐to-‐many rela.onships.
• This allows the data to be modelled correctly in the database
Examples • A customer can rent many DVDs from the LotsoVision store. Each of LotsoVision’s DVDs can be rented to many customers
• An airline company flies many flights, but each flight is flown by only one airline
• The Globex Corpora.on operates many factories. Each of these factories is located in a region. Each region can more than one Globex factory. Each factory employs many employees, but each of these employees is employed by only one factory.
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Data Types
• Character – char – varchar – text
• Date and Time – Date – Time – .mestamp
• Number – bit – integer – real – numeric
• Others – blob – boolean
DBMS
• Database Management System • Goal of a DBMS is to simplify the storage of, and access to data
• Well known DBMS: – Proprietary • Oracle • Access (Microsoa) • SQL Server (Microsoa) • DB2 (IBM)
– Open Source • MySQL • SQLite • PostgreSQL
Database Languages
• Programming languages which are used to – Define a database (i.e. its en..es and the rela.onships between them)
– Manipulate its content (i.e. insert new data and update or delete exis.ng data)
– Conduct queries (i.e. request informa.on based upon defined criteria).
• The Structured Query Language (SQL) is the most commonly used language for Rela.onal Databases – Supported by all rela.onal DBMSs and is a standard.
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SQL
• SQL is split into four sets of commands which are divided based upon the tasks they are used for: – Data Defini.on Language – Data Modifica.on Language – Data Query Language – Data Control Language
Data Defini.on Language
• SQL uses a collec.on of impera.ve verbs whose effect is to modify the schema of the database
• Can be used to add, change or delete defini.ons of tables or other objects.
• These statements can be freely mixed with other SQL statements – so the DDL is not truly a separate language.
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Data Defini.on Language
• CREATE Statement – This Statement is used for crea.ng the database and its objects
• ALTER Statement – This Statement is used for modifying the database and its objects
• DROP Statement – This Statement is used for dele.ng the database and its objects
• TRUNCATE Statement – This Statement is used to delete the data available in a table in a Row-‐By-‐Row manner but with out disturbing its structure
Data Manipula.on Language
• The data manipula.on language comprises the SQL data change statements – Modifies stored data – Does NOT modify the schema or database objects • This is always the responsibility of the Data Defini.on Language
• Used for inser.ng, dele.ng and upda.ng data in the tables of a database
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Data Manipula.on Language
• INSERT Statement – This statement is used for inser.ng data into a table
• DELETE Statement – This statement is used to delete data from a table that matches certain criteria
• UPDATE Statement – This statement is used to update data in a table that matches certain criteria
Data Query Language • The data query language allows users of a database to formulate requests and generate reports
• There is one primary command used in SQL to query the database -‐ the SELECT Statement – This statement is used to query or retrieve data from a table in the database.
– A query may retrieve informa.on from specified columns or from all of the columns in the table
– A query may have specified criteria that must be met in order for data to be returned
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ST3001 – MySQL Tutorial 1 -‐ University of Dublin, Trinity
College
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