Database Beginnings

Database Beginnings CIS 121 – Computer Concepts II Instructor: Ron Christensen

What is Data? • Data are facts about things, places, events • Facts about data are called metadata • Data are building blocks for information CIS 121 - Portland Community College

Common Data Applications • Word Processors – Like fifth generation language, very difficult to track • Spreadsheets – Mostly two dimensional. When items change, multiple spreadsheets become problem some. • Databases – More efficient, real-time, on-line. CIS 121 - Portland Community College

DBMS – Database Management System • DBMS software… • Manages metadata • Organizes data • Enforces security • Manages access to data and metadata • Enforces integrity CIS 121 - Portland Community College

Figure 1.2 Information System Input Output Database CIS 121 - Portland Community College

What is a Database (Black Box)? • A computer accepts input, processes it according to some rules, and makes output. • Everything will be represented as data, including the input and the output • So what the DBMS is doing is taking the data produced (the input) and converting it into information (the output) CIS 121 - Portland Community College

Relational DBMS • Relational refers to the method of organizing data, i.e. in tables • Developed in the1970s • Most common of several different types of DBMS systems • Hierarchical • Network • Object CIS 121 - Portland Community College

Microsoft ACCESS • Relational DBMS software for Windows • Available as part of MS-Office CIS 121 - Portland Community College

Type of Databases • Production Database • Transaction oriented • Lots of well-defined read/write/update actions • Decision Support Database • Query oriented • Complex queries • Few updates or writes CIS 121 - Portland Community College

A Bigger Picture… • Databases are a critical part of information systems • Information systems help people solve problems • Your personal database and web page will form the basis of a personal information system CIS 121 - Portland Community College

Information System Figure 1.2 Software Operating System Application Programs DBMS Write and Use People Database Design and Manage Hardware CIS 121 - Portland Community College

Entities • Entities are anything about which you want to know something • People, places, things, events, concepts • Data are facts about entities CIS 121 - Portland Community College

Entity Sets • Entity sets are collections of relatedentities. Entities are related by their classification: • student entities are related by the fact that they are all students • invoice entities are related by the fact that they are all invoices • car entities are related by the fact that they are all cars CIS 121 - Portland Community College

Entity Sets, cont. • Entity sets are named as a broad definition of the whole entity. • Entity and Entity set names are singular. • Entity and Entity set names are capitalized. Examples: An entity named HR contains HR entities. An entity named EMPLOYEE contains employee records. An entity named DEPARTMENT contains department records. CIS 121 - Portland Community College

Entity Sets, cont. • Entity Sets can only contain related records • a STUDENT entity set may not contain INVOICE data • a DEPARTMENT entity set may not contain invoice data • a PRODUCT entity set may not contain employee data …. And so on CIS 121 - Portland Community College

Relational Databases • Data is stored in TABLES (also called relational sets) • Tables are collections of attributes for related records • The reality is that lots of different things get stuffed into a table for a variety of reasons • (Tables are another word for entity sets) CIS 121 - Portland Community College

Database Tables • A database table is used to store a record (or tuple) • An entity set is a collection of related records • An record is anything you want to keep track of, so an entity may be a person, place, thing, event, etc. • (Record is another word for Entity) CIS 121 - Portland Community College

Database Table Components • At the conceptual level, a database table may be viewed as a matrix. • Matrix rows are also known as tuples or records • each row contains an record • Matrix columns are also called fields or attributes. • Each column (field) contains the record’s attribute values CIS 121 - Portland Community College

Attributes • Attributes are the characteristics that describe records • A STUDENT record may be described by attributes that may include... • social security number • name • address • date of birth • major CIS 121 - Portland Community College

Records, Attributes, Data • Records are things about which you want to know something, e.g. STUDENT • Attributes describe something about the entity, e.g. the name of the student • Data are the values of the attributes, e.g. DOE, JOHN CIS 121 - Portland Community College

Null • A null is an absence of value • A null is NOT • A blank • A zero • A null has several meanings in a database • Value does not exist • Value is not known CIS 121 - Portland Community College

Attribute Names • Attribute names are capitalized. • For documentation reasons, attribute names are composed of two parts: • the first few characters reflect the entity they help describe. • subsequent characters are sufficiently descriptive to identify the attribute. CIS 121 - Portland Community College

Attribute Names, cont. • Examples of attribute names: EMP_LNAME = employee last name STU_GPA = student grade point average PROD_CODE = product code CUST_LNAME = customer last name INV_NUM = invoice number CIS 121 - Portland Community College

Keys • Primary Key (PK) • an attribute (or combination of attributes) that uniquely identifies each row (tuple) in a table. • A PK composed of two or more attributes is known as a composite PK. • Foreign Key (FK) • an attribute in one table whose values match the PK values in a related table or whose “values” are null. • FKs are used to link (connect) related tables. CIS 121 - Portland Community College

Data Integrity. • Entity Integrity • PK uniquely identifies each entity in a table • PK may not include nulls • Referential Integrity • FK values in one table match the PK values in the related table • FK may not include nulls CIS 121 - Portland Community College

A Conceptual View of a Database Table Tables are named. The table you see here is the EMPLOYEE table. Each column contains the values of an attribute. The EMP_FNAME column only contains employee first names; the EMP_PHONE may only contain employee phone numbers. Named attributes (fields) Each row represents an record A row is also called a tuple. Each row/column intersection contains only one of an entity’s attribute values The Primary Key (PK) is a unique record identifier. If you know the PK value, you will know all of its row’s attribute values CIS 121 - Portland Community College

Entity Integrity EMPLOYEE table A table exhibits entity integrity when all of its Primary Key (PK) values uniquely identify each table row (record.) 1. A PK cannot contain duplicate values 2. A PK cannot contains nulls Note: A null indicates the absence of a value; it is not a blank. (You create a null when you tap the ENTER key without first making an entry. A blank is created when you tap the space bar and then tap the ENTER key.) CIS 121 - Portland Community College

Foreign keys (FK) and Referential Integrity A Foreign Key (FK) is an attribute located in one table that “points to” a Primary Key (PK) in a related table. The use of FKs allows you relate one table to another. To maintain referential integrity, a foreign key (FK) must reference an existing PK value in a related table it may be null. INVOICE table LINE table CIS 121 - Portland Community College

Attribute types • Simple (atomic) • Composite • Single-valued • Multi-valued Derived CIS 121 - Portland Community College

Simple (Atomic) Attributes • A simple (atomic) attribute cannot be decomposed into meaningful components • Examples: • The attribute EMP_LNAME cannot be decomposed, because you cannot subdivide EMP_LNAME into a set of new attributes. • The attribute PROD_PRICE cannot be decomposed, because you cannot subdivide PROD_PRICE into a new set of attributes. CIS 121 - Portland Community College

Simple (Atomic) Attributes, cont. Simple attributes may be …. • single-valued or • multi-valued CIS 121 - Portland Community College

Simple (Atomic) Attributes, cont. • Single-valued simple attributes • Example: an employee can have only one gender, so EMP_GENDER is a single-valued attribute. The attribute EMP_GENDER cannot be decomposed, so it is a simple attribute. • Multi-valued simple attributes • Example: an employee can have many degrees, so EMP_DEGREE is multi-valued. The attribute EMP_DEGREE cannot be decomposed, so it is a simple attribute. CIS 121 - Portland Community College

Composite Attributes • A composite attribute can be decomposed into meaningful components • Example: an employee’s address, shown as 123 East Main Street, Nashville, TN 32123 may be decomposed into EMP_ADDRESS = 123 East Main Street EMP_CITY = Nashville EMP_STATE = TN EMP_ZIP = 32123 CIS 121 - Portland Community College

Composite Attributes, cont. A composite attribute may be …. • single-valued or • multi-valued CIS 121 - Portland Community College

Composite Attributes, cont. • single-valued composite attributes • Example: an employee can have only one date of birth, so EMP_DOB is single-valued. But the attribute EMP_DOB can be decomposed into year, month, and day, so it is a composite attribute. • multi-valued composite attributes • Example: an employee can have more than one address, so EMP_ADDRESS may be multi-valued. The attribute EMP_ADDRESS can be decomposed into street address, city, state, and ZIP code, so it is a composite attribute. CIS 121 - Portland Community College

Attribute Storage • Each table row/column intersection contains a single attribute value for a single entity. • Ideally, attributes are simple and single-valued. • Single-valued composite attributes are acceptable • but composite attributes may make queries more complex and may impose reporting limitations. • Multi-valued attributes, either simple or composite, may • create structural problems • make queries more complex and may impose reporting limitations. • May be necessary for a variety of reasons, but should be avoided where possible CIS 121 - Portland Community College

Multi-valued Attribute Storage • Multi-valued attributes are sometimes stored as • strings • this approach yields query complexity and reporting limitations • multiple attributes • this approach yields structural problems • Ideally, multi-valued attributes are handled through the use of composite tables. CIS 121 - Portland Community College

Multi-valued Attributes Stored As Strings Multi-valued attribute Poor practice: Makes it difficult to generate queries such as “How many employees have earned BA or MBA degrees?” CIS 121 - Portland Community College

Storing Multi-valued Attributes In Separate Columns Poor structure: many nulls table structure must be altered when additional degrees are earned CIS 121 - Portland Community College

Composite Tables • Multi-valued attributes can generate many nulls, increasing uncertainty about the data • One solution is to add another table, called a composite table or bridge table • It is often better to use more tables rather than poor attributes in fewer tables CIS 121 - Portland Community College

A Composite Table (EDUCATION) is Used To Convert M:N Relationships To 1:M Relationships Table name: EMPLOYEE Table name: EDUCATION Table name: DEGREE CIS 121 - Portland Community College

Supertype/Subtype Relationships Are Used To Eliminate or Control the Occurrence of Nulls A table with many nulls Supertype. (Table name: EMPLOYEE Subtype. (Table name: PILOT) CIS 121 - Portland Community College

Relationships • Tables can be related to each other in a variety of ways • 1:1 Relationships • 1:M Relationships • M:N Relationships • Recursive Relationships • Tables are related by their PKs and FKs CIS 121 - Portland Community College

1:1 Relationships • Entity in one table is related to only one entity in another table • Example • STUDENT : SOCIAL SECURITY NUMBER Each student has only one Social Security Number, each Social Security Number refers to only one student CIS 121 - Portland Community College

1:M Relationships • Entity in one table is related to many entities in another table • Example • STUDENT : TUITION INVOICE Each student may have several tuition invoices, each tuition invoice is assigned to only one student CIS 121 - Portland Community College

M:N Relationships • An entity can occur more than once on both sides of the relationship – causes several different problems in databases • Example: • STUDENT : CLASS Each student may register for many classes, each class may contain many students CIS 121 - Portland Community College

Some Issues with M:N • May signal redundant data, resulting in anomalies • Modification anomaly • Deletion anomaly • Keep it simple: DO NOT IMPLEMENT M:N RELATIONSHIPS. Use composite tables instead CIS 121 - Portland Community College

Recursive Relationships • Entity is related to itself • Examples • TEAM : TEAM Teams in an athletic league play each other • CLASS : CLASS Some classes are pre-requisites for others CIS 121 - Portland Community College

Optional (vs. Mandatory) Relationships • Optional relationships occur when entities in two tables may be related, but do not need to be. • Example (Optional Relationship): • STUDENT : SOCIAL SECURITY NUMBER A student is not required to have a social security number • Example (Mandatory Relationship) • STUDENT : CLASS A student must be registered in a class to be a student CIS 121 - Portland Community College

End of Lecture CIS 121 - Portland Community College

Database Beginnings