Encyclopedia of Computer Science and Technology

130 database administrationsignal may be amplified or its voltage may be adjusted orscaled to the required level. Another function of signal conditioningis to isolate the incoming signal from the computerto which the acquisition device is connected. Thisis necessary both to protect the delicate computer circuitsfrom possible “spikes” in the incoming signal and to prevent“noise” (extraneous electromagnetic signals created bythe computer itself) from distorting the signal, and thusthe ultimate measurements. Various sorts of filters can beadded for this purpose.The conditioned signal is fed as an analog input into thedata acquisition device, which is often a board inserted intoa personal computer. The purpose of the board is to samplethe signal and turn it into a stream of digital data. Thedigital data is stored in a buffer (either on the board or in thecomputer’s main memory). Software then takes over, analyzingthe data and creating appropriate displays (such as digitalreadings, graphs, or warning signals) as configured bythe user. If the data is being displayed in real time, the speedof the software, the operating system, and the computer’sclock speed may become significant (see clock speed).Performance ConsiderationsThe sampling rate, or the number of times the signal is measuredper second, is of fundamental importance. A highersampling rate usually means a more accurate representationof the physical data (thus audio sampled at higher ratessounds more “natural”). The faster the sampling rate, thelarger the amount of data to be processed and the greaterthe amount of computer resources needed. Thus, picking asampling rate usually involves a tradeoff between accuracyand speed (for a real-time application, data must be processedfast enough so that whoever is using it can respondto it as it comes in).Three internal factors determine the performance ofa DAQ. The resolution is the number of bits available toquantify each measurement. Clearly the ability to measurethousands of voltage levels is useless if the resolution of asystem is only 8 bits (256 possible values.) The range is thedistance between the minimum and maximum voltage levelsthe DAQ can recognize. If a signal must be “squeezed”into too narrow a range, a corresponding amount of resolutionwill be lost. Finally, there is the gain or the ratiobetween changes in the measured quantity and changes inthe signal strength.ApplicationsData acquisition systems are essential to gathering and processingthe detailed data required by scientific and engineeringapplications. The automated control of chemicalor biochemical processes requires the ability of the controlsoftware to assess real-time physical data in order to maketimely adjustments to such factors as temperature, pressure,and the presence of catalysts, inhibitors, or other componentsof the process. The highly automated systems used inmodern aviation and increasingly, even in ground vehicles,depend on real-time data acquisition. It is not surprising,then, that data acquisition is one of the fastest-growingfields in computing.Further ReadingBeyon, Jeffrey Y. LabVIEW Programming, Data Acquisition andAnalysis. Upper Saddle River, N.J.: Prentice Hall, 2000.“Data Acquisition (DAQ) Fundamentals.” Available online. URL:http://zone.ni.com/devzone/cda/tut/p/id/3216. Accessed June8, 2007.James, Kevin. PC Interfacing and Data Acquisition: Techniques forMeasurement, Instrumentation and Control. Boston: Newnes,2000.database administrationDatabase administration is the management of databasesystems (see database management system). Databaseadministration can be divided into four broad areas: datasecurity, data integrity, data accessibility, and systemdevelopment.Data SecurityWith regard to databases, ensuring data security includesthe assignment and control of users’ level of access to sensitivedata and the use of monitoring tools to detect compromise,diversion, or unauthorized changes to database files(see data security). When data is proprietary, licensingagreements with both database vendors and content providersmay also need to be enforced.Data IntegrityData integrity is related to data security, since the completenessand accuracy of data that has been compromisedcan no longer be guaranteed. However, data integrity alsorequires the development and testing of procedures for theentry and verification of data (input) as well as verifyingthe accuracy of reports (output). Database administratorsmay do some programming, but generally work with theprogramming staff in maintaining data integrity. Since mostdata in computers ultimately comes from human beings,the training of operators is also important.Within the database structure itself, the links betweendata fields must be maintained (referential integrity) anda locking system must be employed to ensure that a newupdate is not processed while a pending one is incomplete(see transaction processing).Internal procedures and external regulations mayrequire that a database be periodically audited for accuracy.While this may be the province of a specially trained informationprocessing auditor, it is often added to the dutiesof the database administrator. (See also auditing in dataprocessing.)Data AccessibilityAccessibility has two aspects. First, the system must be reliable.Data must be available whenever needed by the organization,and in many applications such as e-commerce,this means 24 hours a day, 7 days a week (24/7). Reliabilityrequires making the system as robust as possible, such asby “mirroring” the database on multiple servers (which inturn requires making sure updates are stored concurrently).Failure must also be planned for, which means the imple-