INTRODUCTION TO DATABASE MANAGEMENT SYSTEM

Database Manage and Organization

A database is a collection of information that is organized so that it can be easily accessed, managed and updated.

Data is organized into rows, columns and tables, and it is indexed to make it easier to find relevant information. Data gets updated, expanded and deleted as new information is added. Databases process workloads to create and update themselves, querying the data they contain and running applications against it.

Database in Terminology

·         Database

A database is a named collection of tables. (see table). A database can also contain views, indexes, sequences, data types, operators, and functions. Other relational database products use the term catalog.

·         Record

A field is an area in a fixed or known location in a unit of data such as a record, message header, or computer instruction that has a purpose and usually a fixed size. In some contexts, a field can be subdivided into smaller fields. Here are some examples:

·         Command

A command is a string that you send to the server in hopes of having the server do something useful. Some people use the word statement to mean command. The two words are very similar in meaning and, in practice, are interchangeable.

·         Query

A query is a type of command that retrieves data from the server.

·         Table (relation, file, class)

A table is a collection of rows. A table usually has a name, although some tables are temporary and exist only to carry out a command. All the rows in a table have the same shape (in other words, every row in a table contains the same set of columns). In other database systems, you may see the terms relation, file, or even class?these are all equivalent to a table.

·         Column (field, attribute)

A column is the smallest unit of storage in a relational database. A column represents one piece of information about an object. Every column has a name and a data type. Columns are grouped into rows, and rows are grouped into tables. In Figure 1.1, the shaded area depicts a single column.

·         Row (record, tuple)

A row is a collection of column values. Every row in a table has the same shape (in other words, every row is composed of the same set of columns). If you are trying to model a real-world application, a row represents a real-world object. For example, if you are running an auto dealership, you might have a vehicles table. Each row in the vehicles table represents a car (or truck, or motorcycle, and so on). The kinds of information that you store are the same for all vehicles (that is, every car has a color, a vehicle ID, an engine, and so on). In Figure 1.2, the shaded area depicts a row.

·         Figure 1.2. A row (highlighted).

You may also see the terms record or tuple? these are equivalent to a row.

·         View

A view is an alternative way to present a table (or tables). You might think of a view as a "virtual" table. A view is (usually) defined in terms of one or more tables. When you create a view, you are not storing more data, you are instead creating a different way of looking at existing data. A view is a useful way to give a name to a complex query that you may have to use repeatedly.

·         Client/server

PostgreSQL is built around a client/server architecture. In a client/server product, there are at least two programs involved. One is a client and the other is a server. These programs may exist on the same host or on different hosts that are connected by some sort of network. The server offers a service; in the case of PostgreSQL, the server offers to store, retrieve, and change data. The client asks a server to perform work; a PostgreSQL client asks a PostgreSQL server to serve up relational data.

·         Client

A client is an application that makes requests of the PostgreSQL server. Before a client application can talk to a server, it must connect to a postmaster (see postmaster) and establish its identity. Client applications provide a user interface and can be written in many languages. Chapters 8 through 17 will show you how to write a client application.

·         Server

The PostgreSQL server is a program that services commands coming from client applications. The PostgreSQL server has no user interface?you can't talk to the server directly, you must use a client application.

·         Postmaster

Because PostgreSQL is a client/server database, something has to listen for connection requests coming from a client application. That's what the postmaster does. When a connection request arrives, the postmaster creates a new server process in the host operating system.

·         Transaction

A transaction is a collection of database operations that are treated as a unit. PostgreSQL guarantees that all the operations within a transaction complete or that none of them complete. This is an important property?it ensures that if something goes wrong in the middle of a transaction, changes made before the point of failure will not be reflected in the database. A transaction usually starts with a BEGIN command and ends with a COMMIT or ROLLBACK (see the next entries).

·         Commit

A commit marks the successful end of a transaction. When you perform a commit, you are telling PostgreSQL that you have completed a unit of operation and that all the changes that you made to the database should become permanent.

·         Rollback

A rollback marks the unsuccessful end of a transaction. When you roll back a transaction, you are telling PostgreSQL to discard any changes that you have made to the database (since the beginning of the transaction).

·         Index

An index is a data structure that a database uses to reduce the amount of time it takes to perform certain operations. An index can also be used to ensure that duplicate values don't appear where they aren't wanted. I'll talk about indexes in Chapter 4, "Query Optimization."

·         Result set

When you issue a query to a database, you get back a result set. The result set contains all the rows that satisfy your query. A result set may be empty.

Forms of Database

Flat File Database

A flat file database is a database that stores data in a plain text file. Each line of the text file holds one record, with fields separated by delimiters, such as commas or tabs. While it uses a simple structure, a flat file database cannot contain multiple tables like a relational database can. Fortunately, most database programs such as Microsoft Access and FileMaker Pro can import flat file databases and use them in a larger relational database.

Hierarchical Database

A hierarchical database model is a data model in which the data is organized into a tree-like structure. The data is stored as records which are connected to one another through links. A record is a collection of fields, with each field containing only one value. The entity type of a record defines which fields the record contains. A record in the hierarchical database model corresponds to a row (or tuple) in the relational database model and an entity type corresponds to a table (or relation).

Relational Database

A relational database is a collection of data items organized as a set of formally-described tables from which data can be accessed or reassembled in many different ways without having to reorganize the database tables. The relational database was invented by E. F. Codd at IBM in 1970.

Relational database can also be viewed as a set of tables containing data fitted into predefined categories. Each table (which is sometimes called a relation) contains one or more data categories in columns. Each row contains a unique instance of data for the categories defined by the columns. For example, a typical business order entry database would include a table that described a customer with columns for name, address, phone number, and so forth. Another table would describe an order: product, customer, date, sales price, and so forth. 

Examples of Database

·         ADABAS.

·         IBM DB2.

·         Microsoft Access.

·         Microsoft SQL Server.

·         MySQL.

·         Oracle RDBMS.

·         QuickBase.

INTRODUCTION TO SPREADSHEET

INTRODUCTION TO SPREADSHEET

A spreadsheet is an interactive computer application for organization, analysis and storage of data in tabular form. Spreadsheets are developed as computerized simulations of paper accounting worksheets. The program operates on data entered in cells of a table. Each cell may contain either numeric or text data, or the results of formulas that automatically calculate and display a value based on the contents of other cells. A spreadsheet may also refer to one such electronic document.

Spreadsheet users can adjust any stored value and observe the effects on calculated values. This makes the spreadsheet useful for "what-if" analysis since many cases can be rapidly investigated without manual recalculation. Modern spreadsheet software can have multiple interacting sheets, and can display data either as text and numerals, or in graphical form.

Examples of Spreadsheet Package

·         Google Sheets - (Online and free)

·         iWork Numbers - Apple Office Suite.

·         LibreOffice -> Calc (Free)

·         Lotus 1-2-3 (Discontinued)

·         Lotus Symphony - Spreadsheets.

·         Microsoft Excel

·         OpenOffice -> Calc (Free)

·         VisiCalc (Discontinued)

Uses Of Spreadsheet

 History

Although spreadsheets have been used for hundreds of years, the electronic version first appeared in 1978 with a program known as "VisiCalc." In the early 1980's, Lotus 1-2-3 appeared on the scene with Microsoft's Excel debuting a few years later. When Microsoft launched its Windows operating system in 1987, Excel was the first program released for it. "When Windows finally gained wide acceptance with Version 3.0 in late 1989, Excel was Microsoft's flagship product," writes D.J. Power in "A Brief History of Spreadsheets." "For nearly three years, Excel remained the only Windows spreadsheet program, and it has only received competition from other spreadsheet products since the summer of 1992."

Lists

You can create lists, from shopping lists to contact lists, on a spreadsheet. For example, if you entered store items to a spreadsheet along with their corresponding aisles, you could sort by aisle and print before your shopping trip. Your list would provide an aisle-by-aisle overview. The sorting power of spreadsheets becomes more evident when entering more data. Maintaining personal or professional contacts allows you to sort by every field. For example, a salesperson might enter all clients and then sort by zip code allowing him to plan his day with geographic efficiency.

Accounting

Beyond sorting, spreadsheets are invaluable calculators. By entering the appropriate mathematical functions into cells, you can turn a simple spreadsheet into an accounting page. You can list credits in one column and debits in another. The auto-sum feature speeds calculations and can be set up to maintain running totals. And with the flexibility of spreadsheet programs, data used in equations can be anywhere on the sheet or in the workbook. Adding additional pages (sometimes called worksheets) allows you to organize information to suit your needs. Data from anywhere in the workbook can be used in your calculations.

Time Sheets

Besides adding and subtracting integers, spreadsheets can also perform those calculations on time-based numbers. Formatting cells to reflect data as a time (as opposed to simple integers) can allow you to use the spreadsheet as a time sheet. Additionally, you can include descriptions of assorted job functions, employee names, etc. giving you the ability to sort by those to time incurred for any of your chosen fields.

Database Use

Although spreadsheets are not true relational databases, they can be designed and formatted to function as simplified ones. For example, if you need to track pricing of a particular product, enter its price only one time. For all subsequent references to that price, point to the original entry as opposed to re-entering the price. When you need to change the price, change it in its original cell and all corresponding references will update automatically.

Chart Creation

Charts and graphs create better depictions of trends and percentages than raw numbers. As they say, "A picture's worth a thousand words." Spreadsheet programs can automatically convert your data into the visual depiction of your choice, whether it's a pie chart, bar chart or line graph.

Features of Spreadsheet Package and Terms

1.         Row

In Microsoft Excel, a row runs horizontally in the grid layout of a worksheet. Horizontal rows are numbered with numeric values such as 1, 2, 3. Vertical columns are numbered with alphabetic values such A, B, C.

Each row in the worksheet has its own row number which is used as part of a cell reference such as A1, A2, or M16. You can select an entire row by clicking on the row heading (ie: the number running along the left side of the grid layout). In the example above, we have selected row 3.

2.         Column

 A column is a vertical series of cells in a chart, table, or spreadsheet. Below is an example of a Microsoft Excel spreadsheet with column headers (column letter) A, B, C, D, E, and F. As you can see from the picture below, column H is the highlighted column in red and the selected cell D8 is in column D.

3.         Cell

A cell is the intersection between a row and a column on a spreadsheet that starts with cell A1. Below is an example of a highlighted cell in Microsoft Excel; the cell address, cell name, or cell pointer "D8" (column D, row 8) is the selected cell and the locationof what is being modified.

4.         Worksheet

An Excel worksheet is a single spreadsheet that contains cells organized by rows and columns. A worksheet begins with row number one and column A. Each cell can contain a number, text or formula. A cell can also reference another cell in the same worksheet, the same workbook or a different workbook. In Excel 2010, the maximum size of a worksheet is 1,048,576 rows by 16,384 columns.

5.         Workbook

A workbook is an Excel file that contains one or more worksheets. Each of the workbook's worksheets are in separate tabs on the bottom of the Excel window. By default, a new Excel workbook will contain three worksheets. You can switch between worksheets by clicking on the worksheet's tab on the bottom of the Excel window. In Excel 2010 the number of worksheets in a workbook is limited only by your computer's available memory.

6.         Chart

A chart is often called a graph. It is a visual representation of data from a worksheet that can bring more understanding to the data than just looking at the numbers.

A chart is a powerful tool that allows you to visually display data in a variety of different chart formats such as Bar, Column, Pie, Line, Area, Doughnut, Scatter, Surface, or Radar charts. With Excel, it is easy to create a chart.

JOHNNE SYSTEM TECHNOLOGIES SERVICES

Introducing Johnne System Technologies, a home for ICT solutions...
In our firm we undergo several ICT services ranging from: Computer repairs, Computer Networking and Security, Media Service / Live Streaming, Event Coverage, Web-Development and Management, Graphics Design, Printing of Assorted graphics and lots more.... We possess excellent service delivery at a lower rate.

For more details on our service Delivery Contact our Logistics Manager
08030491323..

UNDERSTANDING COMPUTER SYSTEM TROUBLESHOOTING

INTRODUCTION TO HARDWARE TROUBLESHOOTING

Hardware troubleshooting is the process of reviewing, diagnosing and identifying operational or technical problems within an hardware device or equipment. It aims to resolve physical, logical problems and issues within a computing hardware. Hardware troubleshooting is done by hardware or technical support technician.

Hardware troubleshooting processes primarily aim to resolve computer hardware problems using a systematic approach. 

The process starts by first identifying the problem and finding different issues that can cause such a problem and eventually leading to implementing a solution or alternative. 

Hardware troubleshooting is generally done on hardware equipment installed within a computer, server, laptop or related device.

IDENTIFYING HARDWARE PROBLEMS, SOFTWARE PROBLEMS AND CONFIGURATION PROBLEMS

One of the first steps in troubleshooting a computer problem (or any other programmable system problem) is to determine whether the problem is due to a hardware failure or to faulty software. In most computers, you can use a significant event that occurs during the startup process as a key to separate hardware problems from software problems: the single beep that most computer produces between the end of the power-on self test (POST) and the beginning of the startup process.

Errors that occur, or are displayed, before this beep indicate that a hardware problem of some type exists. Up to this point in the operation of the system, only the BIOS and the basic system hardware have been active. The operating system side of the system does not come into play until after the beep occurs.

If the system produces an error message (such as “The system has detected unstable RAM at location x”) or a beep code before the single beep occurs, the system has found a problem with the hardware. In this case, a bad RAM memory device is indicated.

Typically, if the startup process reaches the point at which the system’s CMOS configuration information is displayed onscreen, you can safely assume that no hardware configuration conflicts exist in the system’s basic components. After this point in the bootup process, the system begins loading drivers for optional devices and additional memory.

If the error occurs after the CMOS screen displays and before the bootup tone, you must clean boot the system and single-step through the remainder of the bootup sequence.

You can still group errors that occur before the beep into two distinct categories:

➤ Configuration errors

➤ Hardware failures

A special category of problems tends to occur when a new hardware option is added to the system, or when the system is used for the very first time. These problems are called configuration problems, or setup problems. These problems result from mismatches between the system’s programmed configuration held in CMOS memory and the actual equipment installed in the system.

It is usually necessary to access the system’s CMOS setup utility in the following three situations:

➤ When the system is first constructed.

➤ When it becomes necessary to replace the CMOS backup battery on the system board.

➤ When a new or different option is added to the system (such as memory devices, hard drives, floppy drives, or video display), it might be necessary to access the setup utility to accept the changes that have been implemented.

In most systems, the BIOS and operating system use plug-and-play techniques to detect new hardware that has been installed in the system. These components work together with the device to allocate system resources for the device. In some situations, the PnP logic is not able to resolve all the system’s resource needs and a configuration error occurs. In these cases, the user must manually resolve the configuration problem.

When you are installing new hardware or software options, be aware of the possibility of configuration errors occurring. If you encounter configuration (or setup) errors, refer to the installation instructions found in the new component’s installation/user documentation.

If you cannot confirm a configuration problem, you most likely have a defective component. The most widely used repair method involves substituting known to good components for suspected bad components. Other alternatives for isolating and correcting a hardware failure that appears before the bootup depend on how much of the system is operable.

Normally, symptoms can be divided into three sections: configuration problems, bootup problems, and operational problems.

The system’s configuration settings are normally checked first. It is important to observe the system’s symptoms to determine in which part of the system’s operation the fault occurs. The error messages described in Table below are errors that occur and are reported before the single beep tone is produced at the end of the POST routines.

After the beep tone has been produced in the startup sequence, the system shifts over to the process of booting up and begins looking for and loading the operating system. Errors that occur between the beep and the presentation of the operating system’s user interface (command prompt or GUI) generally have three possible sources. These sources are summarized in the following list that includes the typical error messages associated with each source.

➤ Hardware failure (physical problem with the boot drive)

➤ General Failure Error Reading Drive C:

➤ Corrupted or missing boot files

➤ Bad or Missing Command Interpreter

➤ Non-system Disk or Disk Error

➤ Bad File Allocation Table

➤ Corrupted or missing operating system files

Both configuration problems and bootup problems can be caused by a hardware or operational failure. If the configuration settings are correct, but these symptoms are present, a hardware problem is indicated as the cause of the problem. Conversely, bootup problems are typically associated with the operating system.

HARDWARE TROUBLESHOOTING TOOLS

The general troubleshooting techniques most often performed on a computer hardware is exchanging Failed Replaceable Devices. Due to the relative low cost of computer components, it is normally not practical to troubleshoot failed components to the IC level, like RAM, Hard-disk etc. The cost of diagnosing and repairing small computer devices may be lead to a greater expense.

However, a few hardware diagnostic tools can be very helpful in isolating defective hardware components. These tools include

➤ Software diagnostic disk

➤ Multimeter

➤ Cable tester

➤ POST card

SOFTWARE DIAGNOSTIC PACKAGE

Several commercially available disk-based diagnostic routines can check the system by running predetermined tests on different areas of its hardware. The diagnostic package evaluates the response from each test and attempts to produce a status report for all of the system’s major components. Like the computer’s self-tests, these packages produce visual and beep-coded error messages.

The most common software-troubleshooting packages test the system’s memory, microprocessor, keyboard, display monitor, and the disk drive’s speed. If at least the system’s CPU, disk drive, and clock circuits are working, you might be able to use one of these special software-troubleshooting packages to help localize system failures. They can prove especially helpful when trying to track down non-heat-related intermittent problems.

If a diagnostic program indicates that multiple items should be replaced, replace the units one at a time until the unit starts up. Then replace any units removed prior to the one that caused the system to start. This process ensures that there are not multiple bad parts. If you have replaced all the parts, and the unit still does not function properly, the diagnostic software is suspect.

The final solution and measure that can be established on a computer software, be it application software or System software, is reinstalling the Software to replace the missing or corrupt files. In terms of a malfunctioning Operating System (OS) you reinstall the operating system.

WORKING WITH MULTI-METER

A number of test instruments can help you isolate computer hardware problems. One of the most basic pieces of electronic troubleshooting equipment is the multimeter. These test instruments are available in both analog and digital readout form and can be used to directly measure electrical values of voltage (V), current in milliamperes (mA) or amperes (A), and resistance in ohms. Therefore, these devices are referred to as VOMs (volt-ohmmilliammeters) for analog types, or DMMs (digital multimeters) for digital types.

Figure 3.2 depicts a digital multimeter. With a little finesse, you can use this device to check diodes, transistors, capacitors, motor windings, relays, and coils. This particular DMM contains facilities built in to the meter to test transistors and diodes. These facilities are in addition to its standard functions of current, voltage, and resistance measurement; however, in computer repair work, only the voltage and resistance functions are used extensively.

          A digital Multimeter

The first step in using the multimeter to perform tests is to select the proper function. For the most part, you never need to use the current function of the multimeter when working with computer systems; however, the voltage and resistance functions can be very valuable tools.

In computer troubleshooting, most of the tests are DC voltage readings. These measurements usually involve checking the DC side of the powersupply unit. You can make these readings between ground and one of the expansion-slot pins, or at the system board power-supply connector. It is also common to check the voltage level across a system board capacitor to verify that the system is receiving power. The voltage across most of the capacitors on the system board is 5V (DC). The DC voltages that can normally be expected in a PC-compatible system are +12V, +5V, –5V, and –12V. The actual values for these readings might vary by 5% in either direction.

Note: it is a normal practice to all set the multimeter to its highest voltage range to be certain that the voltage level being measured does not damage the multimeter.

The DC voltage function is used to take measurements in live DC circuits. It should be connected in parallel with the device being checked. This could mean connecting the reference lead (black lead) to a ground point and the measuring lead (red lead) to a test point to take a measurement as illustrated in the figure below. The figure show the DC voltage check on a PC motherboard