File Organization

Chapter 8

Instructor:Pavlos Pavlikas 2

Common File Structure

Serial file: is a file in which the data are physically stored in the order which they were acquired. To retrieve any particular record it is necessary to read through every preceding record. If another record needs to be added it can just added to the end of the file

Instructor:Pavlos Pavlikas 3

Common File Structure

Sequential File: is a serial file in which the data are physically stored in key order.

Random File: the data are not stored in any order. The operation system keeps a map of the disk surface and using this map can go straight to the data. In this way the data is found without reading the whole disk.

Instructor:Pavlos Pavlikas 4

Type of files

Master File Transaction File Backup File Transaction log file

Instructor:Pavlos Pavlikas 5

FILE OPERATIONS

Reading is the operation of taking a copy of a data item from a file.

Writing is the operation of saving any changes to a file. Updating is altering an existing data item already written

in the file. Inserting is adding a new data item to an existing file.

This implies moving all later items to make space. Appending is adding a new item at the end of an

existing file.

Instructor:Pavlos Pavlikas 6

File manipulation

MERGE is to combine two or more ordered data structures, such as files, into a single ordered structure.

SORTING is the process of arranging data items in predetermined order (such as alphabetical or numerical).

Instructor:Pavlos Pavlikas 7

GEOGRAPHICAL INFORMATION SYSTEMS Geographical information systems are systems

which organize data according to location, based on a map. They are powerful tools and need a powerful computer to cope with the processing needed.

Geographical information systems are used by many organizations. They allow data which is difficult to understand to be displayed on a map

Instructor:Pavlos Pavlikas 8

Uses of GIS

1. Providing marketing information for stores. They can display customer density in the surrounding areas as different colors on a map.

2. They can be used by the utility companies (gas, electricity and water) to show where pipes, wires, substations, etc. are located.

3. They are used by BT when deciding where to position new telephone boxes or where to site new transmitters for their mobile telephone network.

4. Local authorities use them to keep data on pavements, lamp posts, road signs, etc. They also use them for planning routes for the emptying of bins and street cleaning.

5. Emergency services (police, ambulance and fire brigade) use them to route vehicles to emergencies via the fastest route.

Instructor:Pavlos Pavlikas 9

Here's an example of how Bank of America used GIS Bank of America used GIS to show the geographic distribution of

the bank's network in relation to deposit potential in the New York City market area. From this analysis, Bank of America can determine where their coverage is strong and where it is weak. Red dots symbolize strong coverage; no dots means coverage is nonexistent.

Instructor:Pavlos Pavlikas 10

Map Quantities

People map quantities, like where the most and least are, to find places that meet their criteria and take action, or to see the relationships between places. This gives an additional level of information beyond simply mapping the locations of features.

Instructor:Pavlos Pavlikas 11

This map shows the number of children under 18 per clinically active pediatrician for a particular study area. It was created by the Center for the Evaluative Clinical Sciences at Dartmouth Medical School as part of an effort to develop a national U.S. database of primary care resources and health services.

Instructor:Pavlos Pavlikas 12

Find What's Nearby

Find out what's occurring within a set distance of a feature by mapping what's nearby.

The Pacific Disaster Center has developed and applied a Vulnerability-Exposure-Sensitivity-Resilience model to map people and facilities (what's nearby) exposed to flood risk in the Lower Mekong River Basin (the feature).