Database management system

A database management system (DBMS) is a software package that allows the user to set up, use and maintain a database. Just as a GIS allows the set up of a GIS application, a DBMS offers generic functionality for database organization and data handling. In the next subsection we take a closer look at what type of functions are offered by DBMSs. Many standard PCs are equipped with a DBMS called  Microsoft Access. This package offers a useful set of functions and the capacity to store terabytes of information.

Reasons for using a DBMS

There are various reasons why one would want to use a DBMS for data storage and
processing:

• A DBMS supports the storage and manipulation of very large data sets. Some data sets are so big that storing them in text files or spreadsheet files becomes too awkward for practical use. The result may be that finding simple facts takes minutes, and performing simple calculations perhaps even hours. A DBMS is specifically designed for these purposes.
• A DBMS can be instructed to guard data correctness. For instance, an important aspect of data correctness is data-entry checking: ensuring that the data that are entered into the database do not contain obvious errors. For instance, since we know in what study area we are working, we also know the range of possible geographic coordinates, so we can ensure the DBMS checks them upon entry. This is a simple example of the type of rules, generally known as integrity constraints, that can be defined in, and automatically checked by, a DBMS. More complex integrity constraints are certainly possible; their definition is is an aspect of the database design. Chapter 8. Spatial data modelling, collection and management
• A DBMS supports the concurrent use of the same data set by many users. Large data sets are often built up over time. As a result, substantial investments are required to create and maintain them, and probably many people are involved in the data collection, maintenance and processing. Such data sets are often considered to have high strategic value by their owner(s) and many people may want to use them within an organization. Moreover, different users may have different views about the data. As a consequence, users will be under the impression that they are operating on their personal database and not on one shared by many people. They may all be using the database at the same time without affecting each other’s activities. This DBMS function is referred to as concurrency control.
• A DBMS provides users with a high-level, declarative query language, with as its most important use the formulation of queries.
• A DBMS supports the use of a data model, which is a language with which one can define a database structure and manipulate the data stored in it. The most prominent data model is the relational data model; this is discussed in full in Subsection 8.4.3. Its primitives are tuples (also known as records, or rows) with attribute values, and relations, which are sets of similarly formed tuples.•
• A DBMS includes data backup and recovery functions, to ensure data availability at all times. As potentially many users rely on the availability of the data, the data must be safeguarded against possible calamities. Regular backups of the data set and automatic recovery schemes provide insurance against loss of data.
• A DBMS allows the control of data redundancy. A well-designed database takes care of storing single facts only once. Storing a fact several times—a phenomenon known as data redundancy—can lead to situations in which stored facts may contradict each other, causing reduced usefulness of the data. Redundancy is, however, not necessarily always problematic, as long as we specify where it occurs so that it can be controlled.

Alternatives for data management

The decision whether or not to use a DBMS will depend, among other things, on how much data there are or will be, what type of use will be made of it, and how many users might be involved. On the small-scale side of the spectrum—when the data set is small, its use is relatively simple, and there is just one user—we might use simple text files and a word processor. Think of a personal  address book as an example or a small set of simple field  observations. Text files offer no support for data analysis, except
perhaps in alphabetical sorting. If our data set is still small and numeric in nature, and we have a single type of use in mind, a spreadsheet program might suffice. This might also be the case if we have a number of field observations with measurements that we want to prepare for statistical analysis.

If, however, we carry out region- or nation-wide censuses, with many observation stations and/or field observers and all sorts of different measurements, one quickly needs a database to keep track of all the data. Spreadsheet programs are generally not suitable for this, however, as they do not accommodate concurrent use of data sets well, although they do support some data analysis, especially when it comes to calculations for a single table, such as averages, sums, minimum and maximum values.

All such computations are usually restricted to a single table of data. When one wants to relate the values in the table with values of another nature in some other table, skilful expertise and significant amounts of time may be required to achieve this.