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Basic Terms and Concepts in Database Technology

This chapter defines the basic terms used in database technology, including fields, records, data occurrences, fixed-length and variable-length records, repeated groups, segments, tree and network models, relational models, and methods of accessing files.

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Basic Terms and Concepts in Database Technology

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  1. File Processing and Data Management Concepts Chapter 12

  2. Define the basic terms used in database technology. Learning Objective 1

  3. These are used interchangeably to denote the smallest block of data that will be stored and retrieved. Introductory Terminology Field Data items Attribute Elements

  4. Introductory Terminology A field may be a single character or number, or it may be composed of many characters or numbers. Customer name Employee social security number Purchase order number Customer account number

  5. Introductory Terminology Logical grouping of fields are called records. An employee A customer A vendor An invoice

  6. Data Occurrences Ocurrences = Instances A record occurrence is a specific set of data values for the record.

  7. Data Occurrences For the record EMPLOYEE (NAME,NUMBER, AGE) we might have the occurrence EMPLOYEE (Brown, 111222333, 33)

  8. Fixed- and Variable-Length Records In a fixed-length record, both the number of fields and the length (character size) of each field are fixed. In variable-length records, the width of the field can be adjusted to each data occurrence. A trailer record is an extension of a master record.

  9. Several Suppliers andWarehouses Example PART_NO PNAME TYPE COST PVEND – the name of the vendor or supplier WARHSE – where the part is stored LOC – the last two digits of the zip code

  10. One Storage Location Example PART (PART_NO, PNAME, TYPE, COST, PVEND #1, WARHSE #1, LOC#1, PVEND #2, WARHSE #2, LOC#2)

  11. Repeated Groups Repeated groups are related groups of fields that repeat themselves in variable-length records. Segments Groups Nodes PART, SUPPLIER, and LOCATION can be written as follows: PART (PART_NO, PNAME, TYPE, COST)

  12. SUPPLIER LOCATION Tree Diagram for PART,SUPPLIER and LOCATION PART

  13. Record Key and File Sequence A key or record key is a data item or combination of data items that uniquely identifies a particular record in a file. Primary sort key Secondary sort key Tertiary sort keys Relative random order

  14. Identify the three levels of database architecture. Learning Objective 2

  15. Database contents Uses of database Desired reports Information to be reviewed Database Management Systems and Their Architecture Conceptual level

  16. Database Management Systems and Their Architecture Logical data structures: Tree (hierarchical) Network Relational Logical level

  17. Database Management Systems and Their Architecture Access methods: Sequential Indexed-sequential Direct Physical level

  18. Conceptual Architecture The Entity-Relationship (E-R) data model is a conceptual model for depicting the relationships between segments in a database. "Entity" instead of segment Attribute refers to individual fields or data items.

  19. Conceptual Architecture The object-oriented modeling technique (OMT) views the components of the system being modeled as object classes. Object class corresponds to a segment. Object corresponds to a particular instance. Inheritance

  20. PLANT_EQUIPMENT ACCOUNT_NO COST DEPRECIATION HEAVY_EQUIPMENT MAINTENANCE_FREQ DATE_PURCHASED HAND_TOOLS USAGE Example of Object-OrientedData Modeling Technique

  21. Compare and contrast the different logical models of databases. Learning Objective 3

  22. Logical Data Structures The relationships that exist between the segments in the database are determined by the logical data structure, also called the schema or database model.

  23. Logical Data Structures What are the three major models of logical data structure? 1. Tree or hierarchical structures 2. Network structures 3. Relational models

  24. Logical Data Structures Tree (hierarchical) model (4 levels and 13 nodes) A B C D E F G H I J K L M

  25. Logical Data Structures Network model (3 levels and 11 nodes) A B C D E F G H I J K

  26. Logical Data Structures Both trees and networks are implemented with imbedded pointer fields.

  27. Implementing Tree andNetwork Structures In a list organization, each record contains one or more pointers (fields) indicating the address of the next logical record with the same attribute(s). A ring structure differs from a list in that the last record in the ring list points back to the first record.

  28. Implementing Tree andNetwork Structures What is a multiple ring structure? In this type of structure several rings pass through individual records.

  29. Location of first record Attribute Index 2 Red 1 Blue Pointer field to next record End of list indicator Records 1 2 4 3 4 5 5  List Structure

  30. Ring Structure Location of first record Attribute Index 2 Va 3 Ky Pointer field to next record Pointer field to first record Records 1 2 4 3 4 5 5 2

  31. Relational Data Structures What is the relational model? It is a logical data structure that views the database as a collection of two-dimensional tables. There are no complicated pointers or lists.

  32. Relational Data Structures Relational algebra Normal forms Normalization

  33. Relational Data Structures What are the three normal forms? First normal form Second normal form Third normal form

  34. Explain the different methods of accessing files. Learning Objective 4

  35. Database Architecture:The Physical Level Sequentially accessed files Indexed files Directly accessed files

  36. Sequentially Accessed Files In a sequential access file, records can only be accessed in their predefined sequence. Sequential file organization is useful when batch processing is required.

  37. Indexed Files An index file is one where an attribute has been extracted from the records and used to build a new file whose purpose is to provide an index to the original file. One important type of indexed file is an indexed-sequential file.

  38. Indexed Files An indexed-sequential file is a sequential file that is stored on a DASD and is both indexed and physically sorted on the same field. These files are frequently referred to as ISAM files.

  39. Indexed Files An ISAM file structurally consists of three distinct areas: The index The prime area The overflow area How would a computer locate a file record whose key is 1002?

  40. Highest key Track index address Track address Highest key on track Record found Structure of an ISAM File Master Index 1500 0300 Track Index Track address 1005 0301 0300 Prime Area Key Data Track address 1002 -------- 0301

  41. Directly Accessed Files Direct-accessfiles allow individual records to be almost instantly retrieved without the use of an index. Each record is assigned to a storage location that bears some relationship to the record’s key values. Most direct-access file systems convert a key to a storage location address.

  42. Randomizing computation (÷ 7) Data records Add remainder to displacement address (10) File storage area Use of a Direct-Access File Processing logic flowchart:

  43. Record Key Remainder after division by seven + Displacement factor (initial address of file area) = Record storage address 1 2 3 4 15 17 11 22 1 3 4 1 10 10 10 10 11 13 14 11  Overflow  Use of a Direct-Access File File loading illustration:

  44. Address Contents … Record 1 KEY 15* … Record 2 KEY 17 Record 3 KEY 11 … … Record 4 KEY 22 … 10 11 12 13 14 15 16 17 18 Range of randomizing computation Overflow indicator Storage allocated for overflow records Use of a Direct-Access File Storage area contents after loading:

  45. Economic Relations betweenFile Organization Techniques The basic economics of file processing are largely determined by the activity ratio. What is the activity ratio? It is the number of accessed records divided by the number of records in the file. The second economic consideration concerns response time.

  46. Economic Relations betweenFile Organization Techniques What is response time? It is the length of time the user must wait for the system to complete an operation. Response time is affected by the physical access time. Another factor that can affect response time is how data records are physically distributed on the disk.

  47. Explain the benefits of database management systems. Learning Objectives 5 and 6 Describe the considerations that are appropriate to the design of computer-based files and databases.

  48. Database Management Systems and Databases in Practice Database Management Systems (DBMS) are computer programs that enable a user to create and update files, to select and retrieve data, and to generate various outputs and reports. All DBMS contain three common attributes for managing and organizing data.

  49. Database Management Systems and Databases in Practice What are these attributes? Data description language (DDL) Data manipulation language (DML) Data query language (DQL)

  50. Why Database Management Systems are Needed DBMS integrate, standardize, and provide security for various accounting applications. In the absence ofintegration, each type of accounting application such as sales, payroll, and receivables will maintain separate, independent data files and computer programs.

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