This chapter gives a brief theoretical preview upon the database information systems and goes through the essence of the problem that should be resolved.
Most of the contemporary Information systems are based on the Database technology as a collection of logically related data, and DBMS as a software system allowing the users to define, create, maintain and control access to the database.
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The process of constructing such kind of systems is not so simple. It involves a mutual development of application program and database. The application program is actually the bridge between the users and the database, where the data is stored. Thus, the well-developed application program and database are very important for the reliability, flexibility and functionality of the system. The so defined systems differentiate to each other and their development comprises a great variety of tasks to be resolved and implemented. The basic idea can be depicted on Figure 1. below: Information System Dbase Queries Retrieve U S E R S Application Program Database Insert DBMS Update Database System Delete i Figure 1. 1 Database information systems - principle scheme Information system suggests a computer technology to be used in order to provide information to users in an organization (for instance), as for the purposes of data transformation into useful information; computer hardware and software are designed and used . A particular case is the Human Resources Information System development.
This kind of systems are responsible for storing data of the staff within an organization and generating reports upon request. -4- Such kind of system could be integrated with other Information systems or modules: Accounting Information System (AIS) – designed to transform financial data into information, or Management Information System (MIS) that provides decision-oriented information to managers, and so on… “Organizations depend on Information Systems in order to stay competitive. Productivity, which is crucial to staying competitive, can be increased through better Information Systems.
This report’s documentation goes through the whole process of both application program and database development. It also comprises the development tools have been utilized for these purposes.
This system should consist of an application program, on one hand, and a database (repository of data) on the other. The program should perform the basic operations upon the database as retrieving, inserting, updating and deleting data. Any additional functionality is a goal of a further module development.
It is a kind of strategy to start the development from designing and constructing the database, as this structure will determine the further structure of the application program. The logical database model (tables, their content and the relationships between them) should respond to the given task and cover the basic requirements. The Interface of the program should be user-friendly, and the program should be as easy for use as it is possible. Both controls and forms should logically and functionally be related within the program and fully respond to the structure of the database.
Another problem is establishing the connections with the database, every time, when a query is needed to be performed upon it. Exception-handling should also be taken into an account during the system’s development due to eventual exceptions that may occur.
The next chapter and its subsections will turn the attention to the method for resolving the problem, the programming environments used for developing the system and the implementation of the operations performed upon the database.
This chapter involves some subsections that concern the basic scheme of resolving the given task and comprise both the methods and tools of its development as well.
At the very commencement, I proceeded to a decision to carry out the development of my task into the following steps:
- Exploring the available development environments and techniques.
- Database Analyzing.
- Database design and Implementation.
- Program’s Structure Analyzing.
- GUI (Graphical User Interface) constructing. 6.
- Bringing all the stuff together (controls data binding and functions implementation).
Each one of these steps could be explained in some brief details as follows:
- Exploring the available development environments and techniques There is a lot of programming environments available to be used for such kind of elaborations. The point is to choose such an environment that we will be able to operate with in a convenient and easy way. This is more or less optional and individual process, that depends on the developer’s experience as well.
- Database Analyzing It concerns all of the demands, put upon the database content and its functionality. The database should be designed and implemented in a way that the user would expect it to be.
- Database design and Implementation This step is tightly related with the previous one as it is completely determined by the requirements, analyzed and discussed in step2.
- Program’s Structure Analyzing The application program as an interface between the users and the database should be an accurate “reflection” of the database on the screen; hence a well analyzed and defined structure is needed.
- GUI Constructing After analyzing the program’s structure and defining what it should consist of, a graphical representation of this stuff is needed in order to enable the user to interact with the data.
- Bringing all the stuff together The next step that should be taken is connecting the program with the database and performing the necessary functionality upon all of the controls.
- Tests To ensure that everything works properly and as it has been expected, test performance has to be done upon the system’s functionality.
The given task concerns a small company (organization). For instance, for the needs of a small company, we could use one set of tools, but for the needs of a larger one, it would be much better if we apply our approach by using some different, that could be more appropriate and would fit much better the requirements we have to satisfy. I decided to use the Access Database Environment as a Database Management System and C# as a programming language for developing my project.
Before proceeding to the explanatory notes of how I have developed the software, I would like to take a preview upon the programming tools (environments) that have been used during this project’s development course. Database Environment: Access is a typical environment for constructing relational databases. The database is the skeleton and the underlying framework of most of the contemporary Information Systems. The evolution of the Database systems could be divided into three phases: the Manual-filing System, the File-based systems, and the Database and the Database Management systems (DBMS). The manual-filing system contains files of information, related to a project, product, task, client, or employee and they are usually labeled and stored in one or more cabinets. The cabinets may be located in the secure area of the building, for safety. To facilitate the process of searching and to find out what we want, more quickly, the different types of item can be put in separate folders and they remain logically related. Actually, the needs of the contemporary industrial world could not be covered or satisfied by using such kind of systems, and especially what concerns their reliability and efficiency. Thus, we historically reach to the second phase of the Database systems evolution – the File-based systems. This kind of systems had been developed in response to the needs and demands of industry for a more efficient data access . The basic idea into the development of this type of systems, is that each Department in an organization (for instance) has an access to its own data (files) through application programs.
It is undesirable as it costs time and money, and takes additional storage space. - Dependency of Data: That’s a kind of inconvenience as the physical structure and storage of the data files and records are defined in the application code. - Data Isolation: It is some difficult to access data, isolated in separate files. Incompatibility of the file formats: It concerns the file structure as a dependent on the programming language, in which one the application program has been developed and implemented, as the file’s structure is embedded in the application program. o After taking a new and more effective approach, the Database and the Database Management System (DBMS) have been created. Most of the contemporary systems are based on the Database technology as a collection of logically related data and the DBMS as a software system allowing the users to define, create, maintain and control access to the Database.
The DBMS is a really powerful set of tools, enabling users to operate easily with data into a database as: Inserting, Updating, Deleting and Retrieving data. It prevents unauthorized access to the database and maintains the consistency of the stored data. The DBMS also restores the data in case of hardware or software failure and reduces the loss of data in this way. MS-Access 2000 (Microsoft Access 2000) is a contemporary development environment for dealing with databases: Access is a computerized management system with relational database. The whole information is stored in separate tables in one file.
Such an information arrangement is more or less convenient as we can view, add and delete information using online forms, and search or retrieve by using queries. The term “Database” comprises collection of objects (tables, forms, pages, queries, macros) for manipulating, retrieving and storing data. It is a very good advantage that the information (data) can be populated in different tables (related to each other) and it is not necessary to store all data into one table. That leads to a less redundancy of data and reduces the required disk storage space, and speeds up processing as well.
There are three relationships between the tables in a database: (one-to-many), (one-to-one) and (many-to-many). One of the mostly used relationships is the (one-to-many) type. If we have a main table (so called Parent table) and some other obedient tables (so called Child tables), then let us assume that the relationship between the parent table and the child tables is of type (one-to-many). It means that every single record from the parent table could have several records into each one of its related child tables. The tables are related by their key-values.
The key into the parent table is called primary key, and the keys into its child tables are called foreign keys. The primary and the foreign key have the same unique value. These conclusions are based on a theory in . The main window-frame of MS-Access can be seen on Figure 1 (Appendix A). -8- C# and the . Net Framework: For the purposes of my project I chose to work with Visual Studio of Microsoft, in particular with the C# as a programming language. My choice is based on the reliable programming environment offered by C# and the highly cleared syntax of this programming language as well.
C# is a good proof for a highly developed modern technology based on the contemporary object-oriented theory in programming and lying on a very powerful, reliable and flexible platform as such as it is the . Net Framework. The main window of the Visual Studio and the . Net Framework basic architecture could be seen on Figure 2: Visual Studio main window and Figure 3: Basic architecture of . Net Framework – Appendix A, : Based on  we can say that the . Net Framework is a development of Microsoft Corporation.
In fact, a lot of efforts, time and investments have been spent on this research and development. As a class library, . Net Framework allows “cross-language” development and can be used by any . Net language to perform different kind of tasks. There are approximately 40 languages with compilers for the . Net Framework, but only some of them are supported by Microsoft Corporation: C#, Visual Basic . Net, C++/CLI, J#, Jscript . Net, Eiffel, and some more. “. Net has several designed intentions: - Interoperability for existing code in COM libraries. Common Runtime Engine: languages compiled to an intermediate language, Common Intermediate Language. - Language Independence: using a Common Type System that defines all possible data-type and programming concepts supported by the CLR (Common Language Runtime). - Base Class Library: also known, as the Foundation Class Library is a l library of types available to all languages using . Net. - Simplified Installation: for the Windows Platform, due to eliminating registry setting and dll-problems. - Security: by letting code execute in different trust levels. ” .
The language of choice – C# as an object-oriented programming language, has a procedural, object-oriented syntax based on C++. It includes some aspects and features of other programming languages as: Java, Visual Basic and Delphi. The developers of C# have emphasized on the language simplification as: fewer symbolic and decorative requirements. -
Analyzing, design and implementation The database for the system should include information of company’s staff, respectively of its employees. The data is subdivided into the following groups: Employees’
I have constructed a database that consists of six data tables. There will be one main table (parent table) and five child tables, related to each other. Patently, for this purpose the necessary primary and foreign keys should be defined into the responding tables.
The so defined structure above is made up in conformity with the user’s needs and demands. Each employee of the staff is intended to have several records, responding to his Working History, Contact Person Information, Salary Information, Time Information and Holiday Information, and only one record containing his basic information within the company – his personal details as: date of birth, gender, marital status, address and phone details, and his current working record.
An employee is supposed to have not only one record of his Working history, or his Contact Person Information….. For instance, if we take a look to the Time Information data table – an employee may have several records in case he has some experience within the current company. It is absolutely the same with the Salary Information, Contact Person Information and Holiday Information data tables. The relationships between the data tables are shown in Figure 4-Appendix A. In Figure 4 we can distinguish six tables that the database consists of.
All of the relationships are of type: “one-to-many”. (For more details about the data tables, see Appendix A: Figure 5 - Parent data table Employee_Details and Child data tables Figure 6, Figure 7, Figure 8, Figure 9, Figure 10). - 11 - The primary key fields could be set to Auto-number data type as Access creates these values in an ascending order to ensure that they are unique within a table. Some of the fields should be “adjusted” to accept null-values. It is quite important to be done as it is tightly related to the input fields of the application program.
I decided to perform it in the following way: those fields that are compulsory to be filled by the user I have set not to accept any null-values of data and on the other hand, those ones, that can be left blank, are set to accept null-values. It is easy to be performed by changing the Allow Zero Length setting (Appendix A: Figure 11 – Setting a data-field to accept nullvalues). It is just needed to go to the desired field that has to be set, and switch between the two options, offered into the “Allow Zero Length” field.
In the example, shown above, the Personal_ID_Number field is set not to allow any null-values thus its field’s length can not be zero as its value is quite essential for identifying an employee as an individual and distinctive person. That has been considered and done for a kind of convenience as the user would wish not to enter all of the data at the moment, and come back later. 2. 4 Program’s Structure Analyzing and GUI Constructing After getting the database prepared, application program should be constructed and implemented in some programming environment to enable the users to communicate with the database.
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