Chapter 12 File Processing and Data Management Concepts

Presentation Outline Terminology Database Technology The Architecture of a Database Management System (DBMS) The Database Administrator

Fixed vs. Variable Length Records I. Terminology Field Data Occurrences Fixed vs. Variable Length Records Record Key Sort Keys

A. Field A field is the smallest block of data that will be stored and retrieved in the information system. Other names for field include data item, attribute, or element. Field 1 Field 2

A specific set of data values for a record in a file. B. Data Occurrences A specific set of data values for a record in a file. 1 2 3 4 5 The above table contains 5 occurrences of account records for the general ledger account file.

C. Fixed vs. Variable Length Records Fixed Length Records Both the number of fields and the length of each field are fixed. Strength: Easier to manipulate records. Weakness: Must accommodate maximum sizes. Variable Length Records Both the number of fields and the length of each field are variable. (See Fig. 15-1 on p. 603) Strength: Less waste of memory when maximum sizes do not have to be accomodated. Weakness: Record manipulation is more difficult.

D. Record Key 1110 1500 2105 2110 A record key is a field or combination of fields that uniquely identifies a particular record in a file.

E. Sort Keys Last Name First Name Age Adams Tom 25 Jones Alisa 36 Primary sort key – The first field used to sort the data occurrences in a record set. Secondary sort key – A field used to determine relative position among a set of data occurrences in a record set. Tertiary sort key – Additional fields beyond primary and secondary sort keys that are required to uniquely identify data occurrences in a record set. Last Name First Name Age Adams Tom 25 Jones Alisa 36 Julie 19 21 Young Sam 22

II. Database Technology The Problem of Redundancy The Components of a Database

A. The Problem of Redundancy That is not what we show per our records. Redundancy occurs when different areas of an organization use the information system to store the same information in more than one place. Results in update anomaly.

B. The Components of a Database Management System Data Description Language (DDL) Data Manipulation Language (DML) Data Query Language (DQL)

1. Data Description Language (DDL) Defines the logical structure of the database (known as the schema). Defines the following: Name of data fields. Type of data (numeric, alphabetic, etc.) Number of positions (length of field). May also define subschema (i.e., individual user views)

2. Data Manipulation Language (DML) Pull a trial balance. The DML consists of the commands for updating, editing, manipulating, and extracting data. Structured query language (SQL) is a common DML in relational settings. Structure Query Language (SQL)

3. Data Query Language Query by Example (QBE) A data query language is a user friendly language or interface that allows the user to request information by simply filling in blanks. Represents a special type of DML.

III. The Architecture of a Database Management System (DBMS) The Database Architecture The Conceptual Architecture and Entity-Relationship (ER) Diagrams Logical Data Structures The Physical Structure

A. The Database Architecture Database contents Uses of database Desired reports Information to be viewed Conceptual Level Logical data structures: Tree Network Relational Logical Level Access Methods: Sequential Access Indexed Files Physical Level

B. The Conceptual Architecture and Entity-Relationship (ER) Diagrams Square boxes are used for entities (separate tables). Ellipses are used for attributes (table columns). Diamond shaped boxes depict relationships. PART_NO NAME COST PART STORED AT LOCATION WHSE ADDRESS

C. Logical Data Structures Tree or Hierarchical Structure Network Structures Relational Structure Selection Projection Join

1. Tree or Hierarchical Structure A parent record can have many children. However a child record can have only one parent. Can only model 1:1 (one-to-one) and 1:* (one-to-many) relationships. Commonly used with accounting data. Can only access data by going from a parent to child. Balance Sheet Assets Liabilities Equity Current Assets Current Liabilities Revenues Long-term Assets Long-term Liabilities Expenses

2. Network Structure Eliminates the distinction of parent and child records. A parent can have many children and a child can have many parents. Can model 1:1 (one-to-one), 1:* (one-to-many), and *:* (many-to-many) relationships. Must know the physical structure of the data in order to access it.

3. Relational Structure Relational databases organize and store data in two dimensional tables consisting of rows and columns. Relationships among tables are represented by common data values in different tables. Straight forward in terms of organizing and searching the data. Possesses ad hoc search capabilities.

3a. Selection Produces a horizontal subset (includes entire row) of a relation which satisfies a boolean predicate. Savings Table Name Acct # Balance John 123 35.75 Bill 205 3.95 Mary 707 7.95 Joe 127 4.05 (Savings) Balance < 5.00 Name Acct # Balance Bill 205 3.95 Joe 127 4.05

3b. Projection Constructs a vertical subset of a relation. The subset is obtained by selecting specified attributes and removing others. Savings Table Name Acct # Balance John 123 35.75 Bill 205 3.95 Mary 707 7.95 Joe 127 4.05 (Savings) Name Balance < 5.00 Name Bill Joe

3c. Join A join is used to combine 2 tables. The attribute used to join must be in both tables. Table R Table S A B C a1 b1 c1 a2 b2 c2 c3 a4 C D E c2 d1 e1 c3 d2 e3 e2 A B C D E a2 b2 c2 d1 e1 e2 c3 d2 e3 a4 R |X| S

D. The Physical Structure Sequential Access Indexed Files

1. Sequential Access Records can only be accessed in a predefined sequence. For example, if there are 100 records in a file, one must access the first 99 records before accessing the last record. Generally useful for batch processing when nearly all records must be accessed.

2. Indexed Files Any attribute can be extracted from the records in a primary file and used to build a new file whose purpose is to provide an index to the original file. First, the index is searched to find a specified value of an attribute such as an customer account number. Second, the disk addresses are used to directly retrieve the desired records See Fig. 12-13 on p. 427.

IV. The Database Administrator This is not quite what we need. The database administrator is a person who coordinates data management activities such as approving the physical contents and user views of the database.

Summary Fields and keys Three Components of a DBMS Three Types of Database Architecture The Database Administrator