Introduction to Database Systems Objectives: Introduction to Database Concepts Introduce Microsoft Access Tables, Queries, Forms, Reports etc Creating a simple database table Indexing

Data, Information, & Database Data : A collection of numbers and text : 273448926 Information : Meaning derived from data SSN # 273-44-8926 Database: A collection of related data stored in a specific format to simplify retrieval. The phone book and dictionary are examples of databases. John Smith’s SSN # 273-44-8926 DBMS – Database Management Systems are programs that help in the storage and retrieval of information from databases. (Access, Oracle)

DBMS Vs. Spreadsheets Store and retrieve data Provide support for data “organizing” and selecting Can do simple calculations Efficient data handling Customers of VISA with balance > 1000 Store and analyze data Provide support for complex calculations Can do simple data organizing and selecting Inefficient data handling What was the net profit of VISA

Access DBMS Objects

Access DBMS “objects”: Tables - a list of data organized into fields and records Queries - question structures to sort, filter and select specific information Forms - structures for screen views of data Reports - structures for written output of data Program Modules - program code to perform specific actions

A Database Management System Data Tables Relationships Data Input: Onto Tables Onto Forms From files Reports Query Results DBMS Queries Output Files Program Modules

An Inventory Database System Forms: Order Transactions New Vendors & New Customers New Products Shipments Program Modules Tables: Current Inventory Customer Accounts Vendor List Orders Order Details Program Modules Customer Invoices Daily Ship List Accounts Payable Inventory Low Message Reports & Queries Output File:

“Objects”: Tables Data is stored in objects called Tables Data on tables are listed in rows called records A record consists of one or more ordered categories called fields Field types include Text. Number, Currency, Date etc. Certain fields are required fields and must be filled Field Properties – format, validation rule, required, size, masks, defaults, ranges A table is a listing of multiple records, all records in a table have the same fields

Primary Key A field, or combination of fields, which uniquely identifies a record in a database

Table Datasheet View: Bank Customers Record Field Primary Key

A Second Table - “Transactions” keeps track of all deposits and withdrawals What’s the Primary key on this table?

Walkthrough: Setting up a Table using Design View

Divide Tables into Inseparable Fields Address as 1 field – 17 Main St. New York, New York 10002 Address as 4 fields Street Address - 17 Main St. City - New York State - New York Zip code – 10002 If you wanted to filter the table to get a list of only New York City residents how would this work with these two different Table structures

Defining Properties for each Field in a Table For a person’s social security number use: What field type? Text, Number - Short Integer, Number- Long Integer etc. Should it be optional or required? Does the value need to be within certain limits or from a predefined list? Is there a default value? Would an input mask be appropriate

Memory and Field Size Why adjust the field size for Social security number? Text: Up to 255 characters Memo: Up to 65,535 characters Numbers: Integer - 2 bytes - 16 bits Long Integer - 4 bytes - 32 bits (*) Byte (character) - 1 byte Single - 4 bytes - -precision 7 Double - 8 bytes - -precision 15

How should you decide what information goes on which table? If a fact appears in more than one record of a table, then this fact should probably be defined in another table. Example: Account number Each fact change should change in only one place Example: Address Calculations shouldn’t be part of the database Example: Current Balance Select a Primary Key where applicable so you can relate your tables

Tools: Sorting and Filtering Sorting - allows the user to temporarily order the records by a specific field Ascending or Descending order Single or multiple sort fields Filtering - allows the user to view only specific records that meet the criteria Filter by form or filter by selection Specify a single criteria or use Boolean and/or for multiple criteria in multiple fields

Storing and Retrieving Records from Tables How are DBMS systems designed to efficiently handle data? Data is stored on magnetic or optical disk in a linear fashion To retrieve a specific record one would have to search them one at a time until the desired record is found. To make data retrieval more efficient one can “index” a table based on a specific field. Search routines could then be used on that field to more efficiently find the record Example: Alphabetically sorting a dictionary and then analyzing the first letter of the criteria in the sorted list.

Linear Search on Un-indexed Field Find the name of student for ss#606147775 Go to the first record to see if 178301771 matches 606147775. If no match then check the next record until a match is found. Here it must check 11 items before you find the correct one. On average it will have to check #entries/2

A Binary Search on an Indexed Field Find name of student for ss#606147775 This table is sorted by SSN First go to the middle record of the table and compare values to see if 606147775>328824082. If it is greater, continue checking only from this midpoint to the end. Otherwise continue checking only from the beginning to the midpoint Then go to the midpoint of this subsection. The process continues until a match is found Indexing can aid in querying efficiency using algorithms such as binary search (1/2,1/2 again) vs. a linear search (1 at time from top to bottom). A binary search cuts the processing time significantly for large databases

Indexing vs. Sorting Sorting your table & saving permanently changes the record order.. Use an index instead. ssn#606147775 is associated with record 14

From Tables to a Relational Database We have carefully looked at tables in our database how to set them up, define fields etc. The real advantages of a DBMS however are in their ability to relate information. Thus far we have customer names on one list and transactions on a separate list. How do we match a customer’s name to specific transaction? We need a way to relate these two tables to extract useful information. We can relate these two tables by matching the account numbers.

One to Many Relationship Acct#/Account No. is the Foreign Key

A Foreign Key is a field that defines the relationship between 2 tables: A valid foreign key must have all of the properties listed below: Must be a primary key (unique) in at least one of the tables The field names on each table do not have to match as long as the information is the same. Fields with the same name does not necessarily mean they are the foreign key. The related fields must be the same data type (number, text etc)

Walkthrough: Establishing relationships Primary Key on Accounts table: acct# Foreign Key: acct#/Account#

Once Relationships are established you can gather information from one or more tables to answer questions like: Create a list of account numbers and owner names and total transactions What are the total deposits made by accounts starting with 5? What is the total balance of all accounts held by Jane Doe ? These requests are known as Queries

“Objects”: Queries To extract information from the Database use a Query which is a “question” or “request” The query is not the data that results but a set of instructions specifying how specific records or combinations of records should be extracted - it lets the user: prepare lists, sort, filter choose records to met specific criteria do calculations on the data Summarize data by a specific grouping match up the data to related information

Walkthrough: A Simple Query Create a query to list the first name, last name and transaction amount for each transaction Design: Dynaset Result: We will spend the next 1-2 weeks learning, in greater detail, how to use the query tool.

Walkthrough: Setting up a form “Objects”: Forms A form is not data that results but a set of instructions specifying a screen view format of the data. These forms are designed to simplify data display, inputting and editing. Walkthrough: Setting up a form

Walkthrough: Setting up an AutoReport “Objects”: Reports A report is not the data that results but a set of instructions specifying the format of written output. Reports allow users to vary : The type of text formatting Report & Page headers, footers, titles Which data fields (from tables, queries and/or calculations) to be used Sorts, Filters, Groupings of fields Walkthrough: Setting up an AutoReport

Sample Report: Transactions by Customer

“Objects”: Macros &Modules Programmed instructions updating tables/queries from inputs customer address account balance retrieving data from other sources performing tasks if a certain criterion is met monthly bank statement balance > 20000 send letter offering estate planning service This course will not cover the Macros & Modules - we can refer you to more Advanced books on Access & Visual Basic

A Review of Database Theory Information is stored in objects known as tables consisting of records or related information categorized into fields. A field that uniquely identifies a table is known as a primary key field Tables can be related to each other using valid foreign key fields. Queries, Reports, Forms are objects which can be created using the data on tables to dynamically extract/display information in a specified format.