Review -Chapter 4 Entity relationship (ER) model Steps for building a formal ERD Uses ER diagrams to represent conceptual database as viewed by the end user Three main components Entities Relationships Attributes Includes connectivity and cardinality notations Includes weak vs strong entities and relationships Connectivity and cardinalities are based on business rules Review -Chapter 4 In the ER Model, M:N relationship is valid at conceptual level ERDs may be based on many different ER models including Chen and the Crowsfoot. Database designers are often forced to make design compromises Conflicting goals of data base design are a challenge of balancing design standards against processing speed and information requirements. Database design is iterative rather than linear or sequential process 1 2 Review -Chapter 5 Extended Entity Relationship (EER) model adds semantics to ER model via entity supertypes, subtypes, and clusters Generalization/Specialization Hierarchies Specialization hierarchy depicts arrangement and relationships between entity supertypes and entity subtypes Inheritance allows an entity subtype to inherit attributes and relationships of supertype Disjoint subtypes Entity Clustering & Virtual Entities Entity cluster is virtual entity type used to represent multiple entities and relationships in ERD Review -Chapter 5 Selecting Primary Keys Natural keys are identifiers which exist in the real world Surrogate primary keys are useful when there is no natural key for a primary key Composite keys are useful to represent M:N relationships and weak (strong-identifying) entities In a 1:1 relationship, place the PK of mandatory entity as foreign key in optional entity 3 4 1
Review -Chapter 5 Design Traps Time-variant data refers to data whose values change over time and whose requirements mandate that you keep a history of data changes Fan trap occurs when you have one entity in two 1:M relationships to other entities and there is an association among the other entities that is not expressed in model Data modeling checklist provides way for designer to check that the ERD meets set of minimum requirements Review -Chapter 6 Normalization & its role in database design Normalization is technique used to design tables in which data redundancies are minimized Normal forms most commonly encountered. 1NF, 2NF, 3NF Boyce-CoddNormal Form is a refinement of 3NFd 4th Normal Form - deleting Multi-valued attributes Normalization is an important part of the design process Whereas ERD s provide a macro view, normalization provides micro view of entities Focuses on characteristics of specific entities May yield additional entities 5 6 Review -Chapter 6 Formal Normalization properties Table is in 1NF when all key attributes are defined and when all remaining attributes are dependent on primary key Table is in 2NF when it is in 1NF and contains no partial dependencies Table is in 3NF when it is in 2NF and contains no transitive dependencies Table that is not in 3NF may be split into new tables until all of the tables meet 3NF requirements In Practice it is difficult to separate normalization from E-R diagramming designers will use both techniques. DML -Data manipulation language commands Select, Insert, Update, Delete, Commit, Rollback DDL commands -Data definition language commands Defines basic data base objects & manipulates their structures. DDL Commands -DBA Only: Create Database/Schema/Tablespace DDL Commands Create Table When defining attributes in a table, a column name and data type are required. 7 8 2
Create Table cont d When defining attributes in a table, a column name and data type are required. Attribute data typing The ANSI standard data types are supported by all RDBMS vendors in different ways Table Constraints Constraints used on columns including Not Null, Check, Default, and Unique. Constraints used on tables include Primary Key and Foreign Key. Create View Virtual tables or Views can be created to select pertinent columns from an existing table. Create Synonym Granting access rights Create Index -An index is a special object associated with a table which allows more efficient retrieval based on another key. Alter modifies the existing table structure Allows Adding column(s), Dropping columns or constraints, and Updating constraints. Drop deletes a database object Other Rename creates a new Table structure, insert the data from the original table, then drop the original table. Grant/Revoke allows giving privileges to other users for tables you own. Synonym creates shorter aliases for existing tables. Comment allows information about a table or column to be stored in the database. 9 10 More DML Commands Update Insert Delete A database transaction - Commit & Rollback includes all commands between a Commit (or session start) and the next Commit (or normal end of session). A copy of a table can be made by using a Create Table with a nested query to copy Column Data from the original table. Joining tables Standard or Natural join -uses join condition to match only rows with equal values in specified columns Cross join - creates a Cartesian product Recursive join -joining a table with itself Outer joins -are used to select rows that have no matching values in other related table Left Right Full -selects rows with no matching values from both tables in addition to the rows with matching values 11 12 3
Sequences a DB object used to auto-generate values which can then be assigned to a column s data. SQL built-in Functions -used to extract or transform data Numeric Character Date Data conversion Non-data typed functions (misc. & psuedocolumns) Updatable Views only using simple joins. No aggregate functions or set operators Relational Set Operators -part of the new SQL- 99 extensions. Union eliminates duplicate rows Union All retains duplicate rows Intersect combines rows from two queries, returning only rows in both queries Minus -combines rows from two queries, returning only rows appearing in the 1 st but not the 2 nd query. 13 14 Adv. ANSI standard Join Operators Cross Join Cartesian product Natural Join returns rows with matched columns having matching values Join Using -specify only the join column, therefore named the same in both tables Join On specify both table s join column, so can be differently named. Left/Right Outer Join returns matching rows & unmatched rows in Left/Right table. Full join returns both matched and unmatched rows. Not available in previous syntax. PL/SQL - Procedural Code Allows both SQL statements and 3GL control structures. A cursor is used to handle multiple rows returned by a SQL statement inside PL/SQL code. Embedded SQL refers to use of SQL statements within an application programming language Types of persistent procedural code stored in the database. Triggers executed based on events to a table. Procedures allows parameter input/output 15 16 4
Functions allows parameter input, and a single return value, and is executed by another trigger or procedure. Non- stored/persistent Procedural code Anonymous Blocks unnamed sets of code, not stored but for immediate execution Reading only -Not Covered in Class - Advanced - Nesting selects with Correlated queries as Attributes On the From clause On the Where clause On the Having clause 17 5