File Design
FILE DESIGNInformation systems in business are file and
database oriented.
Data are accumulated into files that are proces...
File Components
• Data Item
Individual elements of data are called data items also known as
fields or simply items. For ex...
File Components (example)
RECORD NAME DATA ITEM NAME TYPE
LENGTH
Bank cheque Cheque Originator c 90
Cheque Number N
6
Date...
Fixed and variable Length
Records
Fixed length records
When the number and size of data item in a record are
constant for ...
Record Key
• To distinguish one specific record from another,
systems analysts select one data item in the record
that is ...
Entity
• An entity is any person, place, thing, or event
of interest to the organisation and about
which data are captured...
File and Database
File
A file is a collection of related records. Each record in a
file is included because it pertains to...
File Organization
Records are stored in files using a file
organisation that determines how the
records will be
• Stored
•...
Sequential Organization
• Sequential organisation is the simplest way
to store and retrieve records in a file.
• In a sequ...
Sequential Organization
(Reading)• To read a sequential file, the system always
starts at the beginning of the file and re...
Sequential Organization
(Searching Record)
• Records are accessed in order of their appearance in the file.
• E.g to find ...
Direct-Access
Organisation
• In contrast to sequential organisation,
processing a direct-access file does not require
the ...
Direct-Access
Organisation
(Direct Addressing)
• In the cheque example, the direct access of records
is demonstrated by us...
Direct-Access
Organisation
(Direct Addressing)
• It knows that the key serves as the address
and thus goes directly to the...
Direct Access Organization
(Drawbacks-Direct
Accessing)
• Storage must be allocated even though it will
go unused.
• Anoth...
Direct Access Organization
(Hash Addressing)
• When direct addressing is not possible but direct access is
necessary, the ...
Direct Access Organization
(Hash Addressing-contd..)
• A separate overflow area is set aside to provide for
record storage...
Indexed Organisation
• A third way of accessing records is through an
index.
• The basic form of index included a record k...
Indexed Organisation
(Characteristics)
• An index is a separate file from the master file to which it
pertains. Each recor...
Indexed Sequential
Organisation
• The one most widely used in information systems, creates a
pseudo sequential file. Group...
Indexed Sequential
Organisation (Example)
Record Key Starting Block Address
1115 1345
1315 1349
1429 1346
1725 1350
Indexed Sequential
Organisation (Example)
1346
1349
1350
Overflow
blocks
1010 1011 101
3
101
4
1017 1019 111
0
1113 1115
1...
Inverted File
• The other type of data structure commonly used in
database management systems is an inverted file.
• This ...
OUTPUT DESIGN
• One of the most important features of an
information system for users is the output it
produces.
• Outputs...
Output Objectives
• Convey information about past activities,
current status or projections of the future e.g.
- a report ...
Key Output Questions
• Who will receive the output ?
• What is its planned use ?
• How much detail is needed ?
• When and ...
Contents of the Outputs
Data Items
The name of each data item along with its
characteristics should be recorded in a stand...
Contents of the Outputs
(Contd..)
Data Totals
There is often a need to provide totals at
various levels. Their source must...
Contents of the Outputs
(Contd..)Data Editing
It is not always desirable to print or display
data as it is held on a compu...
Contents of the Outputs
(Contd..)
Output Media
Systems analyst also has to determine the most
appropriate medium for the o...
Contents of the Outputs (Contd..)
Considerations while selecting Media
• Suitability of the device to the particular
appli...
Developing A Printed Output Layout
• The design of printed output will determine
its usefulness to the recipient.
• An out...
Developing A Printed Output Layout
(Contd..)
The layout should show the location and
position of the following.
• All vari...
Developing A Printed Output Layout
(Contd..)
Common notations used in designing an
output layout :-
• Variable information...
Designing Printed Output
• Headings
In every report- title of the report, date and
time should be included to tell the use...
Designing Printed Output
(Contd..)
• Column Headings
Before actually marking in the data fields,
enter the column headings...
Designing Printed Output
(Contd..)
• Data & Details
Enter the description of the data below the
column headings, using the...
Guidelines for Report
Design
(Summary)• Reports and documents should be designed to
read from left to right and top to bot...
INPUT DESIGN
Introduction
Input Specification describes the manner in
which data enter the systems for processing.
Input d...
Objectives of Input Design
• Controlling Amount Of Input
Data preparation and data entry operations
depend on people. Beca...
Objectives of Input Design
(Contd..)
• Avoiding Delay
Avoiding processing delays resulting from
data preparation or data e...
Objectives of Input Design
(Contd..)• Avoiding Extra Steps
When the volume of transactions can't be
reduced, the analyst m...
Summary (Lecture 8)
• File Design
• Output Design
• Input Design
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itft-File design

  1. 1. File Design
  2. 2. FILE DESIGNInformation systems in business are file and database oriented. Data are accumulated into files that are processed or maintained by the system. The systems analyst is responsible for designing files, determining their contents and selecting a method for organising the data.
  3. 3. File Components • Data Item Individual elements of data are called data items also known as fields or simply items. For example bank cheque consists of the following data items ,check number, date, payee, numeric amount, script amount, note, bank identification, account number, and signature. • Record The complete set of related data pertaining to an entry, such as a bank cheque is a record Treated as a single unit. The bank cheque is therefore a record consisting of seven separate fields related to the payment transaction. Each field has a defined length and type (alphabetic, alphanumeric, or numeric)
  4. 4. File Components (example) RECORD NAME DATA ITEM NAME TYPE LENGTH Bank cheque Cheque Originator c 90 Cheque Number N 6 Date 8 Payee C 24 Amount N 8,2 Bank Number N 9 Account Number N
  5. 5. Fixed and variable Length Records Fixed length records When the number and size of data item in a record are constant for every record, the record is called a fixed length record. The advantage of fixed-length record is that they are always of the same size.Thus, the system does not have to determine how long the record is or where it stops and the next one begins, thus saving processing time. Variable-length records Variable Length records are less common in most business applications than fixed-length designs because the latter are easier to manage and meet most application needs. Record size may vary because the individual data items vary in length (each record can have a different number of bytes)or because the number of data items in a record changes from one occurrence to another.
  6. 6. Record Key • To distinguish one specific record from another, systems analysts select one data item in the record that is likely to be unique in all records of a file and use it for identification purposes. • This item, called the record key, key attribute, or simply key, is already part of the record, not additional data added to it just for the purpose of identification. • Common examples of record keys are the part number in an inventory record, the chart number in a patient medical record, the student number in a university record, or the serial number of a manufactured product. Each of these record keys has various other uses in the organisation or
  7. 7. Entity • An entity is any person, place, thing, or event of interest to the organisation and about which data are captured, stored, or processed. Patients and tests are entities of interest in hospitals, while banking entities include customers and cheques.
  8. 8. File and Database File A file is a collection of related records. Each record in a file is included because it pertains to the same entity. A file of cheques, for example, consists only of cheques. Inventory records and invoice do not belong in a cheque file, since they pertain to different entities. Databases A database is an integrated collection of data. Records for different entities are typically stored in a database (whereas files store records for a single entity). In a university database, for example, records for students, courses, and faculty are interrelated in the same database.
  9. 9. File Organization Records are stored in files using a file organisation that determines how the records will be • Stored • Located • Retrieved
  10. 10. Sequential Organization • Sequential organisation is the simplest way to store and retrieve records in a file. • In a sequential file, records are stored one after the other without concern for the actual value of the data in the records. • The first record stored is placed at the beginning of the file. The second is stored right after the first ( there are no unused positions), the third after the second, and so on. This order never changes in sequential file organisation, unlike the other organisations to be discussed
  11. 11. Sequential Organization (Reading)• To read a sequential file, the system always starts at the beginning of the file and reads its way up to the record, one record at a time. For example, • if a particular record happens to be the tenth one in a file, the system starts at the first record and reads ahead one record at a time until the tenth is reached. It cannot go directly to the tenth record in a sequential file without starting from the beginning. • In fact, the system does not know it is the tenth record. Depending on the nature of the system being designed, this feature can be an
  12. 12. Sequential Organization (Searching Record) • Records are accessed in order of their appearance in the file. • E.g to find location of cheque 1258 in a sequential file, we will call the cheque number 1258, the search key. • The program controls all the processing steps that follow. • The first record is read and its cheque number compared with the search key: 1240(Let it be first) versus 1258. Since the cheque number and search key do not match, the process is repeated. The cheque number for the next record is 1244, and it also does not match the search key. • The process of reading and comparing records continues until the cheque number and the search key match. If the file does not contain a cheque numbered 1258, the reading and comparing process continues until the end of the file is reached.
  13. 13. Direct-Access Organisation • In contrast to sequential organisation, processing a direct-access file does not require the system to start at the first record in the file. • Direct-access files are keyed files. They associate a record with a specific key value and a particular storage location. • All records are stored by key at addresses rather than by position; • if the program knows the record key, it can determine the location address of a record and retrieve it independently of every other record in the file.
  14. 14. Direct-Access Organisation (Direct Addressing) • In the cheque example, the direct access of records is demonstrated by using a storage area that has a space reserved for every cheque number from 1240 to 1300. • The system uses the cheque number as a physical record key. • Cheque number 1248 is stored at address 1248, the location reserved for the cheque with that number. • To retrieve that cheque from storage in a computer system, the program is instructed to use the number 1248 as the search key.
  15. 15. Direct-Access Organisation (Direct Addressing) • It knows that the key serves as the address and thus goes directly to the assigned location for the record with the key of 1248 and retrieves the record. • The attractive feature of direct organisation is that records are retrieved much more quickly than when the file must be searched from the beginning. • When storage is assigned for the file, it starts at the lowest key value and extends to the highest key value.
  16. 16. Direct Access Organization (Drawbacks-Direct Accessing) • Storage must be allocated even though it will go unused. • Another problem prohibiting use of direct addressing arises when the keys for the records do not match storage addresses. Even if the analyst wants to use direct addressing, it is impossible to do so if key values and addresses do not correspond. For example, if keys contain characters (e.g., a key of AB1CD) in direct addressing is not possible, since there is no address for AB1CD.
  17. 17. Direct Access Organization (Hash Addressing) • When direct addressing is not possible but direct access is necessary, the analyst specifies the alternative access method of hashing. • Hashing (also called key transformation or randomising) refers to the process of deriving a storage address from a record key. • An algorithm (an arithmetic procedure) is devised to change a key value into another value that serves as a storage address. (The data value in the record itself does not change.) • There is no perfect hashing algorithm, although some are much better than others when it comes to minimising synonyms. • In practice, synonyms occur when the hashing procedure is applied on different keys and produces the same address in storage.
  18. 18. Direct Access Organization (Hash Addressing-contd..) • A separate overflow area is set aside to provide for record storage when synonyms occur. When a record is stored, the hashing algorithm is performed and the address derived. • The program accesses that storage area, and, if it is unused, the record is stored there. If there is already a record stored there, the new record is written in the overflow area. When the system must retrieve a record, the hashing algorithm is performed and the storage address determined. Then the record in the storage area is checked. If it is not the correct one (meaning that a synonym occurred earlier), the system automatically goes to the overflow area and retrieves the record for processing.
  19. 19. Indexed Organisation • A third way of accessing records is through an index. • The basic form of index included a record key and the storage address for a record. • To find a record when the storage address is unknown (as with direct address and hashing structures), it is necessary to scan the records. However, the search will be faster if an index is used, since it takes less time to search an index than an entire file of data.
  20. 20. Indexed Organisation (Characteristics) • An index is a separate file from the master file to which it pertains. Each record in the index contains only two items of data: a record key and a storage address. • To find a specific record when the file is stored under an indexed organisation, the index is first searched to find the key of the record wanted. When it is found, the corresponding storage address is noted and then the program accesses the record directly. • This method uses a sequential scan of the index, followed by direct access to the appropriate record. The index helps speed the search compared with a sequential file, but it is slower than direct addressing. When the master file is not in any specific order , this method of file organisation is indexed non- sequential organisation. There is one entry in the index for every record in the master file.
  21. 21. Indexed Sequential Organisation • The one most widely used in information systems, creates a pseudo sequential file. Groups of records are stored in blocks with a capacity for a specified amount of data. • For example, the blocks can store up to 3150 pieces of data. The first block, starting at address 1345, is in sequential order. • The master file stores individual blocks of records in sequential order. This is not a sequential file, however, since all the records are not stored in physically adjacent positions; think of it as a file of separate, full or partially full blocks, each in sequential order. • The adjacent blocks are not in ascending order. For example, to pursue a logical ascending sequence, the record following 1115 at the end of the first block is in the block at address 1349.
  22. 22. Indexed Sequential Organisation (Example) Record Key Starting Block Address 1115 1345 1315 1349 1429 1346 1725 1350
  23. 23. Indexed Sequential Organisation (Example) 1346 1349 1350 Overflow blocks 1010 1011 101 3 101 4 1017 1019 111 0 1113 1115 1316 1317 132 1 132 3 1324 1410 141 4 1415 1417 1418 141 9 1427 1428 142 9 1117 1121 112 0 121 0 1211 1212 121 5 1217 1218 1221 131 0 1311 1313 131 5 1510 1521 152 2 161 7 1619 1620 172 1 1724 1725 1345
  24. 24. Inverted File • The other type of data structure commonly used in database management systems is an inverted file. • This approach uses an index to store information about the location of records having particular attributes. • In a fully inverted file, there is one index for each type of data item in the data set . Each record in the index contains the storage address of each record in the file that meets the attribute. • Some data items in a database will probably never be used to retrieve data. Therefore, no index will be built for those data items. If not all attributes are indexed, the database is only partially inverted, which is more common data structure.
  25. 25. OUTPUT DESIGN • One of the most important features of an information system for users is the output it produces. • Outputs from computer systems are required primarily to communicate the results of processing to users. • Without quality output, the entire system may appear to be so unnecessary that users will avoid using it, possibly causing it to fail. • The term output applies to any information produced by an information system
  26. 26. Output Objectives • Convey information about past activities, current status or projections of the future e.g. - a report on stock in hand shows current status, exception report e.g. for electricity billing number of houses locked in a area. • Signal important events, opportunities problems or warnings • Trigger an action e.g. reorder level report whether printed or displayed. • Confirm an action e.g. report of goods received
  27. 27. Key Output Questions • Who will receive the output ? • What is its planned use ? • How much detail is needed ? • When and how often is the output needed ? • By What Method ?
  28. 28. Contents of the Outputs Data Items The name of each data item along with its characteristics should be recorded in a standard form: - • Whether it is alphabetic or numeric Valid and specific range of values e.g. minimum, maximum fixed values or ranges. • Size of data item • Position of decimal point, arithmetic sign or any other indicator The objective is to present the same data item being referred to by various names or the same name being used to describe different items
  29. 29. Contents of the Outputs (Contd..) Data Totals There is often a need to provide totals at various levels. Their source must be identified and they must be defined and registered as data items. The systems analyst must specify :- • At what level(s) they are required e.g. subtotal, grand total. • The position e.g. at the end of line. • What will cause them to occur e.g. change of key or any other condition
  30. 30. Contents of the Outputs (Contd..)Data Editing It is not always desirable to print or display data as it is held on a computer. The systems analyst must know whether the form in which it is stored is suitable for the output. So if any editing is required he must specify it e.g. • Decimal points to be inserted or not. • Where the currency symbol should appear as prefix or suffix. • Alignment of items e.g., right, left.
  31. 31. Contents of the Outputs (Contd..) Output Media Systems analyst also has to determine the most appropriate medium for the outputs. This will involve consideration of wide range of devices including • Line Printer • Graph plotter • V D U • Magnetic Media • Microfilm
  32. 32. Contents of the Outputs (Contd..) Considerations while selecting Media • Suitability of the device to the particular application. • The need for hard copy and number of copies required. • The response time required. • The location of users • The S/W and H/W available. • The cost.
  33. 33. Developing A Printed Output Layout • The design of printed output will determine its usefulness to the recipient. • An output layout is the arrangement of items on the output medium. When analysts design an output layout, they are building a mock up of the actual report or document as it will appear after the system is in operation.
  34. 34. Developing A Printed Output Layout (Contd..) The layout should show the location and position of the following. • All variable information • Item details • Summaries and totals • Separators e.g. dash & underline, control breaks • All pre-printed details • Headings • Document name • Organisation name and address • Instructions • Notes & comments
  35. 35. Developing A Printed Output Layout (Contd..) Common notations used in designing an output layout :- • Variable information • X to denote that an alphabet or special character *,/ will be printed or displayed. • 9 to denote a number will be printed. • Constant information The information written on the form as it should appear when printed.
  36. 36. Designing Printed Output • Headings In every report- title of the report, date and time should be included to tell the users what they are working with and on what date it was prepared. The page number provides quick reference for the users who work with data found at various locations throughout the report.
  37. 37. Designing Printed Output (Contd..) • Column Headings Before actually marking in the data fields, enter the column headings. It is a good practice to use an underline, dash or some other symbol to separate the column headings from the start of data. Every column should have a heading that describe its contents.
  38. 38. Designing Printed Output (Contd..) • Data & Details Enter the description of the data below the column headings, using the X and 9 conventions explained earlier and indicate size of data item. • Summaries Some report designs specify summary information, column totals or subtotals. Label all titles and headings as you wish them to appear, denote variable data by X or 9 and indicate the maximum length of the field.
  39. 39. Guidelines for Report Design (Summary)• Reports and documents should be designed to read from left to right and top to bottom. • The most important items should be easiest to find e.g. in an inventory report Item Number is the most important item. It is placed in the first column. • All pages should have a title and page number and show the date the output was prepared. • All columns should be labelled. • Abbreviations should be avoided.
  40. 40. INPUT DESIGN Introduction Input Specification describes the manner in which data enter the systems for processing. Input design features can ensure reliability of system and produce results from accurate data. The input design also determines whether the user can interact efficiently with the system.
  41. 41. Objectives of Input Design • Controlling Amount Of Input Data preparation and data entry operations depend on people. Because labour costs are high, the cost of preparing and entering data is high, so reducing data requirements can lower costs. The computer may sit idle while data are being prepared & input for processing. By reducing input requirements, the analyst can speed the entire process from data capture to processing.
  42. 42. Objectives of Input Design (Contd..) • Avoiding Delay Avoiding processing delays resulting from data preparation or data entry operations should be one of the objectives of the analyst in designing input. • Avoiding Errors In Data The rate at which errors occur depends on the quantity of data, since the smaller the amount of data fewer the opportunities for errors. The analyst can reduce the number of errors by reducing the volume of data that must be entered for each transaction.
  43. 43. Objectives of Input Design (Contd..)• Avoiding Extra Steps When the volume of transactions can't be reduced, the analyst must be sure the process is as efficient as possible. Such input designs that cause extra steps should be avoided. • Keeping The Process Simple There should not be so many controls on errors that people will have difficulty using the system. The system should be such that it is comfortable to use while providing the error control methods.
  44. 44. Summary (Lecture 8) • File Design • Output Design • Input Design

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