ERM to SQL

Abstraction Layers Conceptual –What data is held An Image and its meta-data Entity-Relationship model (ERM) Logical –How data is organised in storage Block and Directory structure Tables, keys Physical –How data is stored in bits JPEG as a stream of bytes A Database as files and records stored in a DBMS-specific format Abstraction Realisation (Refinement Reification) (Reverse Engineering) (Engineering, Model-Driven development

QSEE

Case Tool - QSEEQSEE is a free download for individual use is available in the lab (older version  ) enables a wide range of diagram types to be created –UML –Data flow diagrams … –Entity-relationship diagram With generation of SQL for creating a database (with some fixes  - use Perl script to clean up)

ER Model to RDBMS QSEE will produce 2 types of schema –XML DTD XML schema –SQL Relational Database with different targets: ORACLE MySQL Microsoft SQL server SQL 2 standard

RDBMS target Each entity becomes a table Each attribute becomes a column of a table Each relationship become common fields and values in two tables. –Two cases One-many Many-many

Primary Key An attribute which has a different value for every entity instance – ‘Unique’. May be a combination of several attributes – Composite Primary Key. Index on this attribute created by the database May need to be created if no attribute is unique and stable – Auto-increment. Primary keys are the glue of a relational database.

One-many relationship Each one-many relationship is implemented by adding the primary key of the entity on the one side (the parent) as new columns on the many (the child) side This added column is known as a ‘foreign key’ –So Image gets a new column called ‘memberid’ a foreign key constraint defines the relationship When an image is added to the database, the appropriate value of memberid for the creator is added to the image record (a common value)

Relationship in RDBMS M1 P4P5P1 M2 P3 P9 P7 M3 pkM1 pkM2null pkM2 MemberPhoto

Generated SQL DDL CREATE TABLE Member( memberidINTEGER NOT NULL, name VARCHAR(20), PRIMARY KEY (memberid) ); CREATE TABLE Photo( photoidINTEGER NOT NULL, image64MEDIUMBLOB, memberidINTEGER NOT NULL, PRIMARY KEY (photoid), FOREIGN KEY (memberid) references Member(memberid) );

Using a foreign key To find all the Photos belonging to member M2 Select * from photo where memberid=‘M2’ To find the creator of photo P1 Select member.name from photo natural join member where photoid=‘P1’

Foreign Key integrity What happens when you add a Photo –The memberid on the Photo record must reference an existing Member What happens when a member is deleted –Don’t allow it if she has any photos : ‘RESTRICT’ –Delete all her photos as well : ‘CASCADE’ –Set the memberid to NULL ALTER TABLE Photo ADD INDEX (memberid), ADD CONSTRAINT fk1_Photo_to_Member FOREIGN KEY(memberid) REFERENCES Member(memberid) ON DELETE RESTRICT ON UPDATE RESTRICT;

Many-many relationship

G1 P4P5P1 G5 P3P7 G2 pkG1 pkP1 pkG2 pkP1 pkG1 pkP4 pkG5 pkP4 pkG2 pkP5 pkG1 pkP7 GroupPhoto GroupPhoto GroupPhoto

Adding a link table CREATE TABLE Tag( tagNameVARCHAR(40) NOT NULL, PRIMARY KEY (tagName) ); CREATE TABLE Photo_Tag( photoidINTEGER NOT NULL, tagNameVARCHAR(40) NOT NULL, PRIMARY KEY (photoid,tagName), INDEX(photoid), FOREIGN KEY(photoid) REFERENCES Photo(photoid) ON DELETE RESTRICT ON UPDATE RESTRICT, INDEX(tagName), FOREIGN KEY(tagName) REFERENCES Tag(tagName) ON DELETE RESTRICT ON UPDATE RESTRICT );

QSEE tasks Handles the addition of foreign keys Creates link tables for many-many relationships So let QSEE do the work –If a primary key changes, the database definition will be updated automatically –Integrity Constraints generated for you

‘Weak entities’ Entities whose existence depends on the existence of one or more ‘parent’ entities’ –Typically this is a one-many relationship –If the parent is deleted, so are the children –The primary key of the parent becomes a column in the child (foreign key) AND this column is part of the primary of the CHILD –Denoted in the ERM by a bar across the relationship

Emp-dept is a bit more complicated

SQL DDL for emp-dept -- Create a Database table to represent the "Emp" entity. CREATE TABLE Emp( empnoINTEGER NOT NULL, enameVARCHAR(12), jobVARCHAR(12), hiredateDATE, salDECIMAL(8,2), commDECIMAL(8,2), deptnoINTEGER NOT NULL, mgr_empnoINTEGER NOT NULL, -- Specify the PRIMARY KEY constraint for table "Emp". -- This indicates which attribute(s) uniquely identify each row of data. CONSTRAINTpk_Emp PRIMARY KEY (empno) ); ALTER TABLE Emp ADD CONSTRAINT fk2_Emp_to_Emp FOREIGN KEY(mgr_empno) REFERENCES Emp(empno) ON DELETE RESTRICT ON UPDATE RESTRICT;

EmpnoEname 7369SMITH 7499ALLEN 7521WARD 7566JONES 7654MARTIN 7698BLAKE 7782CLARK 7788SCOTT 7839KING 7844TURNER 7876ADAMS 7900JAMES 7902FORD 7934MILLER Select Mgr from Emp where Sal between 2000 and 3000 Select Empno, Ename from Emp Find the names of the managers of employees who earn between 2000 and 3000 E M EmpnoMgrDeptno

Find the names of the managers of employees who earn between 2000 and 3000 Select Ename From Emp E, Emp M Where E.mgr=M.empno and E.sal between 2000 and 3000 Mgr Empno Ename KING Distinct(Ename)

Target is XML

Target XML Here the names of columns and entities are included in the data. The relationship between member and images is containment – all the images for a member occur immediately after the details of the member herself Same ER model but different implementations in different technologies.

Tutorial Generate a database for the KML folder/placemark/style Clean up the generated code –Remove Use statement Comments starting ---- –Use a text editor or if possible the Perl script Use PhpMyAdmin to create this database in your mySQL account