Information system analysis and design Dr. Dina Tbaishat

Recap Last lecture we started with the second phase in a system development life cycle – design According to Kendall and Kendall (2002) , we mentioned that Design can be for: effective input, effective output, databases, user interface, and data entry procedures Last week we covered the input, output and data entry design, today we shall look at database design

introduction Data storage is basic in information systems To design a good data storage in an information system some objectives should be met, these are: Assuring purposeful information retrieval Efficient data storage Availability of data Efficient updating and retrieval Data integrity

Basic concepts Entity: “an object or event about which someone chooses to collect data” (Kendall and Kendall, 2002). Entities are drawn using rectangles Relationships: associations between entities Entity Relation Diagram (ERD): a diagram that shows the tables (relations) and their relationships Cardinality of a relationship: refers to the nature of the relationship between tables, it is the number of instances of entity B that can be associated with entity A

Other notations for the cardinality: 1 to many 1 *

Attributes: characteristics of entities, things that describe entities Records: data items that have something in common with the entity described. These are for one instance of the entity This table is for the entity (student): Address ID Last name First name Amman 2783623 Mazen Layla Zarqa 1829277 Khalaf Hoda 2738262 Salem Ali 1726382 Smith John

Relational databases are preferred over flat databases since they have no empty records and do not have repeated records Typical data types are text (that is, alphabetic characters) number date/time Why is it important to assign a data type for fields ??

The data type indicates the operations that can be performed on the field, for example, having numerical data allows arithmetical operations to be performed on the data Similarly, using the data type ‘date’ allows data to be sorted chronologically Defining a data type for fields can help prevent the wrong type of data being entered. If a field is defined as containing text data (for instance), the program can perform checks on any data entered to make sure it is the right kind

Using keys… Linking the records in separate tables requires the use of keys A key uniquely identifies each record of a table. The simplest way to create a key is to create a column with serial numbers so each entity has a unique value for that field A table may have more than one key for example student number and student's nationality number but one key is chosen to be a primary key

Foreign key: is a field (or collection of fields) in one table that uniquely identifies a row of another table, for example, adding “course-key” to the “student table”

SQL When you search a large website for information, for instance when you search a large e- government site, very often, behind the scenes, a large relational database is being searched SQL is used for extracting information from a database SQL stands for Structured Query Language For example, suppose we wanted to find the family names of all students whose average is 2: SELECT family-name FROM student WHERE GPA=2

Viewing data Generally data is viewed in a ‘form’, which is a specially designed interface between the user and the database There are usually rectangular boxes to show the fields’ values for certain record (patient or student) The user can scroll forwards and backwards though the records, or search on any field for a particular piece of data Fields are usually labeled for ease of identification, for example, student name: These labels are design features of the form; they need not be the same as the entity names or attribute names

Good DB design Break your data into logical pieces (but not too much – name and phone number) Always have a primary key Apply normalization, by having no repetitive data. If a table has more than 20 fields, re- think! Do not use short column names, make it meaningful Pay attention to data types Pay attention to constraints! Always test it

exercise Create ERD for registration process at your university, think of the appropriate tables (entities), their attributes and the possible relationships

References Kendall, K. E., & Kendall, J. E. (2002). Systems analysis and design. USA: Pearson Education