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Transcript
Relational Database Design DSC340 Mike Pangburn Difficulties of Managing Data Data are scattered and collected by many individuals using various methods and devices. Data come from many sources including internal sources, personal sources and external sources. Vast amounts of data can be collected and processed e.g., Amazon.com collecting clickstream data. What is a relational database? You have all heard of the major players in the RDBMS (relational database mgmt system) market E.g., Oracle, MySQL, Microsoft SQL-Server What makes a database relational? Relational db’s are organized around _______ Earlier database systems (“hierarchical”, “network”) were harder to use, and never developed the popularity of relational systems Database Design terminology Entity is a kind of thing you want to store information about (e.g., students, courses, buildings, etc.). Attribute is a characteristic or quality of a particular entity Note: same idea as a class attribute in programming – a piece of information out an object Primary key is a field that uniquely identifies that record. Foreign keys are fields that have reflect identifying information from another entity (allowing you to “look up” the associated entity). What are relationships between entities? A relationship between 2 database entities represents the possibility that two entities may be associated with each other E.g., a customer may rent a video There are 3 basic types of relationships: 1-to-1 1-to-Many Many-to-Many Relationship types One-to-one when a single instance (row) in the first table can be related to at most one row in the second table, and vice versa One-to-many when a single instance (row) in the first table can be related to many rows in the second table, AND when a single instance (row) in the second table can be related to at most one row in the first table Many-to-many when a single instance (row) in the first table can be related to multiple rows in the second table, and vice versa Relationship types Examples below for one-to-many and many- to-many Store (storeId) Owns Video (videoId) 101 3 Customer Video (accountId) PreviouslyRented (videoId) 115 101 123 123 102 145 103 5 145 12 90987 104 90987 13 99787 99787 The database design process A good order in which to ask yourself some questions… What real-world entities (“things”) am I collecting information about? Each entity will become a table (think of a table as a list of things) What pieces of information (attributes) about those entities do I wish to store? Also, what subset of that information will be used to identify the things (e.g., SSN would be a common choice for a table containing people things) How are the entities related? We need a key (an “identifier”) for the things in each table (list) Table Plausible Identifier (a “key”) Customer of brick-and-mortar video store account ID Online customer of video store e-mail address Working person in the United States Social Security number DVD video 12-digit UPC bar code number In the last case (books), you might need to track specific copies. A simple design example You and several of your bird-loving neighbors want to keep track of the birds that come to feed in the various yards in the neighborhood. What things are we collecting information about? Each implies a separate database table What entities are in the bird-study problem? Birds Birdfeeders Yards List (table) of Yards 2 1 3 Yards Yard Number Owner 4 Address Phone Number List (table) of Birdfeeders Bird Feeders Bird Feeder Number Material (Wood, Plastic, Metal) Location in Yard (Sun, Partial/Full Shade) Table of Birds Bird Data Data Number Date Time Bird Type # of this type Relationship: One Yard, Many Feeders There must be one field in both tables that is the same, so that the database knows how the tables connect. In this case, we need to know which yard each bird feeder is located. Bird Feeders Bird Feeder Number Material Location in Yard Yard Number ∞ Each Yard can have many Birdfeeders, but each Birdfeeder can only be in one Yard. This is called a one to many (1 - ∞) Relationship. 1 Yards Yard Number Owner Address Phone Number Relationship: One Birdfeeder, Many Birds Bird Data Again, there must be one field in both tables that is the same, so that the database knows how the tables connect. In this case one birdfeeder can be visited by many birds. Data Number Date Time Bird Type Bird Feeder Number ∞ Bird Feeders Most relationships in the world (of data) turn out to be One-to-Many. 1 Bird Feeder Number Material Location in Yard Yard Number More details on Implementing relationships One-to-one Add a foreign key column to one of the tables E.g., consider a university where each faculty member has one office, and each office holds one faculty member Two design option: (1) include an “Room Num” foreign key column in the faculty table, or (2) include a “Fac SSN” foreign key column in the rooms table These two tables show the first design option: Faculty Rooms Fac SSN Fac Name Fac Phone Room Num 046-25-5834 John Roon 506-3998 382 156-99-5933 Bill Hill 506-9322 2913 190-03-1944 Kiefer Zorn 506-4927 122 076-55-6822 Pinzer Mohan 506-9399 1001 Foreign Key column Room Num Building Type 122 West Hall Office 382 Condon Hall Office 1001 High Tower Office 2913 Gurt Building Office 2940 Gurt Building Class More details on Implementing relationships One-to-many Add a foreign key column to the table on the “many” side E.g., painter and paintings exhibit a 1-to-many relationship To capture the relationship, we add a “painter id” column to the painting table Painting Painter ID Name Deceased Sex 2 Tore Rasmussen No M 3 Raechel Niel Yes F 4 Jon Smyth Yes M 5 Philis Stonips No F Code Title Est. Value Type PID 100 A Sense of Space $2000 Water 2 101 The Road to Nowhere $3000 Water 2 102 Reflections $80,000 Oil 3 103 A Journey’s End $55,000 Oil 4 104 Fisherman’s Catch $40,000 Oil 4 105 Reflections $45,000 Oil 4 106 Treescape $5000 Oil 5 107 Veiled Visions $4000 Oil 5 Foreign Key column More details on Implementing relationships Many-to-many Add a bridge table “between” the two table which keeps track of all row combinations E.g., at a university, the relationship between Students and Classes is many-to-many One student can enroll in multiple classes One class will have multiple students Classes Students Student SSN Student Name Student Phone Class Num Term Room Num Time 046-25-5834 Cosmo Rinker 541-844-9001 754 F05 2940 MW 8am 089-43-5569 Doogie Rupp 541-911-3579 755 F05 2940 MW 10am 076-55-6822 Wendy Kooper 541-074-4031 802 S06 2940 TTh 8am 075-83-9931 Curtis Ponzol 513-567-6772 813 S06 2940 TTh 10am Adding a column to either table (or both) will not be adequate to represent many students taking one course, and one course having many students, so we need to add a “bridge table” Why don’t we do this? Classes Class Num Term Room Num Time Students 754 F05 2940 MW 8am 046-25-5834, 089-435569 755 F05 2940 MW 10am 802 S06 2940 TTh 8am 813 S06 2940 TTh 10am Students Student SSN Student Name Student Phone Classes 046-25-5834 Cosmo Rinker 541-844-9001 754, 802 089-43-5569 Doogie Rupp 541-911-3579 076-55-6822 Wendy Kooper 541-074-4031 075-83-9931 Curtis Ponzol 513-567-6772 Implementing relationship types Adding a “bridge table” to handle the many-tomany relationship it’s just a 2 column table of data!-nothing special! Students The Enrollment “bridge table” below relates Students and Classes! Student SSN Student Name Student Phone 046-25-5834 Cosmo Rinker 541-844-9001 089-43-5569 Doogie Rupp 541-911-3579 Enrollment 076-55-6822 Wendy Kooper 541-074-4031 Student SSN Class Num 075-83-9931 Curtis Ponzol 513-567-6772 046-25-5834 754 046-25-5834 755 075-83-9931 755 Classes Class Num Term Room Num Time 075-83-9931 802 754 F05 294 MW 8am 075-83-9931 813 755 F05 211 MW 10am 089-43-5569 802 802 S06 111 TTh 8am 089-43-5569 813 813 S06 211 TTh 10am 076-55-6822 754 076-55-6822 802 Basic Database Design rules-of-thumb Information about different real-world entities should be stored in different tables Splitting different kinds of information across different tables is referred to as “normalized” design in the database realm Design should store information using the smallest logical parts E.g., would it be better to have Street, City, State, ZIP fields rather than one Address attribute? Each part defines a column Design should not store derived attributes Calculate derived values as needed E.g., would it be better to store birth-date or age ? Design should not cause blank (null) values Implementing a database design Once you have designed the set of tables you want to comprise your relational database, you need to create the same within a RDMS (Relational Database Management System) or equivalent For example, we could implement the Students, Classes, and Enrollment tables We will use an online database system at reports.zoho.com After your design is implemented, you can create SQL queries to extract your information from your database design We will discuss SQL next class Databases and SQL will be the focus of the next hw
