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characters can be coded), including alphabetic, numeric, and special signs, are represented using six positions of binary notation (plus a parity bit position). The Extended Binary Coded Decimal Interchange Code (EBCDIC) uses eight binary positions for each character format plus a position for parity checking (256 characters can be coded). The American Standard Code for Information Interchange (ASCII) is a seven-bit code that offers 128 possible

Сcharacters. ASCII was developed by users of communications and data processing equipment as an attempt to standardize machine-to-machine and system-to-system communication.

Computer Number Systems and Conversions. Representing a

иdecimal number in binary numbers may require very long strings of ones and zeros. The hexadecimal system is used as a shorthand method to represent them. The base of this system is 16, and the symbols used are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F. In other words, F is 15 in decimal notation and 1 1 1 1 inбАbinary.

Programming Languages Techniques. Assembler languages are closer to machine instructions than to human language, and having to express logical procedures, arithmetical calculations, and textual manipulations in these languages affects a programmer's productivity because they are so cumbersome. There are many higher-level programming languages, such as ALGOL, BASIC, COBOL, FORTRAN, and Pascal, that are much closer to human means of expression.

A programmer writes a source program in a human-readable programming language. A compilerДtranslates these English-like statements into instructions that the computer can execute—such instructions are called an "object program." Through added library routines the computer does further processing of the object program, executes it, and an "output" is produced. There are some "optimizing compilers" that automatically correct obvious inefficiencies in source programming.ИSometimes, with the use of "interpreters," debugging can be done to a program as it executes the user program piece by piece. MUMPS, LISP, and APL are interpreters used for this purpose in the health care environment, artificial intelligence, and mathematics fields, respectively. Because of the time and costs associated with development, it is generally not cost effective in today's environment to develop an application package, but rather buy it (if available) from a vendor. The costs are thus spread among thousands of users. Typical applications packages used for public health purposes are SAS and SPSS (for biostatistics) and ArcView/GIS (for Geographical Information Systems). In addition there are some data manipulation languages (e.g., Oracle and dBASE) that were written with this purpose. A database manipulation language (DML) is a special sublanguage used for handling data storage and

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retrieval in a database system. Using a data definition language (DDL), programmers can organize and structure data on secondary storage devices.

Data Acquisition. Capturing and entering data into a computer is expensive. Direct acquisition of data avoids the need for people to read

values and measure, encode, and/or enter the data. Automated data acquisition can help eliminate errors and speed up the procedure. Sensors Сconnected to a patient convert biological signals into electrical signals that

are transmitted into a computer. Many times these signals (e.g., ECG, blood pressure, heart rate) are analog signals, and in order to be stored into a digital signal a conversion needs to occur. This process is called analog to digital иconversion (ADC).

DATABASES AND DATABASE

MANAGEMENT SYSTEMS

A databaseбА(DB) system is a computer-based record keeping system used to record and maintain certain types of information that have a significant value to some organization. A DB is a repository of stored data, which in general is both integrated and shared. Between the physical database and the users of the system is a layer of software, usually called the database management system (DBMS). All requests from the users to access the DB are handled by the DBMS.

When trying to organize the data and information within an organization, the DB helps the userДin entering, storing, and retrieving it, and when trying to integrate all or part of the information of the enterprise the DB becomes a key player. Normally, within the DB, information is organized into data elements, fields, records, and files. In a system such as a hospital information system (HIS), a patient name is a data element or a field; a record could be related to that patient's visit onИa particular date (e.g., date, diagnoses, treatments, charges, medications, tests) at a particular time; and a file would contain all the information from all the visits for that patient. An HIS DB will include not only patient files, but it could also have accounting information related to charges, inventory, payroll, and personnel records. With DB systems, different people can have access to different parts of the system, so, for example, not all personnel employees will have access to laboratory results.

The DBMS organization and definition of the contents of the individual data elements, fields, records, and files are provided via a machine-readable definition called "schema." This creates an independence of physical location from logical location of the content of a DB. The DBMS not only "manages the DB" but also allows for entering, editing, and retrieving results. The

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DBMS helps with the integration of data coming from multiple sources. The user can also access and retrieve specific types of information via queries.

A DB provides an organization with centralized control of its operational data. Some of the advantages of having centralized (versus distributed) control of the data are:

Due to technological advancements, databases today are much more complex than a few decades ago. They contain "multimedia" information, such as text, graphics, scanned images from documents, clinical images from all modalities (X-rays, ultra-sound, MRI, CT scan), still and dynamic studies, and sound. When doing population studies, the creation of data "warehouses" is necessary, and data "mining" techniques are used to extrapolate results. In public health, the data needed for a study can reside in a small computer, in a local area network (LAN), or in a wide area network (WAN). In order to use information that is geographically distributed (and/or with distributed users) it is important to learn techniques for data integration and data communications. Because of the continuing fusion of computers and

INTERNET AND

THE WORLD WIDE WEB

There is little historical precedent for the swift and dramatic growth of the Internet, which was originally a limited scientific communication network developed by the U.S. government to facilitate cooperation among federal researchers and the university research community. With its rapid adoption by the private sector, the Internet has remained an important research tool, and it is also becoming a vital ingredient in maintaining and increasing the scientific and commercial leadership of the United States. In the twenty-first century, the Internet will provide a powerful and versatile environment for

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business, education, culture, entertainment, health care and public health. Sight, sound, and even touch will be integrated through powerful computers, displays, and networks. People will use this environment to work, study, bank, shop, entertain, visit with each other, and communicate with their health care providers. Whether at the office, at home, or traveling, the environment and its interface will be largely the same, and security,

Сreliability, and privacy will be built in. Benefits of this dramatically different environment will include a more agile economy, improved health care (particularly in rural areas), less stress on ecosystems, easy access to lifelong and distance learning, a greater choice of places to live and work, and more иopportunities to participate in the community, the nation, and the world.

Internet and WWW Acronyms. People that communicate with each other electronically may not have the same "platform." "Cross-platform" means that people do not have to use the same kind of operating system to access filesбАon a remote system. In order to access the Web there are two basic mechanisms: (1) using the telephone system to link to another computer or network that is connected to the Internet, and (2) connecting to a network; and from there into the Internet. An Internet service provider (ISP) may be required to access the Internet. An important factor regarding Internet access is bandwidth, which determines how much data a connection can accommodate and the speed at which data can be accessed.

Information on the Web is generally written in Hypertext Markup Language (HTML), which is a text-based markup language that describes the structure of a Web document's content andДsome of its properties. It can also be viewed as a way of representing text and linking it to other resources, such as multimedia files, graphic files, still or dynamic images files, and sound files. HTML contains the information or text to be displayed and the control needed for its display or playback.

File Transfer Protocol (FTP), a cross-platformИprotocol for transferring files to and from computers anywhere on the Internet.

Gopher, a tool for browsing files on the Internet.

Usenet, a worldwide messaging system through which anyone can read and post articles to a group of individuals who share the same interests.

Wide Area Information Server (WAIS), one of a handful of Internet search tools that can be spread across the network to scour multiple

archives and handle multiple data formats.

Hyperlink (also called link), a pointer — from text, from a picture or a

graphic, or from an image map — to a page or file on the World Wide

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Web; hyperlinks are the primary way to navigate between Web pages and among Web sites.

Today, a Web browser is the main piece of software required by the end user to find information through Internet. Some of the most popular browsers

are: Lynx, Mosaic, Netscape Navigator/Communicator, and Internet Explorer. Lynx is a text-only Web browser; it cannot display graphical or Сmultimedia elements. Mosaic, a graphical Web browser, was the first "full-

featured" graphical browser for the Web. It was developed by a team of programmers at the National Center for Supercomputing Applications (NCSA). One of these programmers, Marc Andreesen, later formed Netscape. Netscape Navigator/Communicator is one of the most popular Web browsers. Internet Explorer is Microsoft's Web browser.

Web Resources. A Uniform Resource Locator (URL) is a Web resource that describes the protocols needed to access a particular resource or site on

computers communicate over a network. Protocols link clients and servers together and handle requests and responses, including making a connection, making a request, and the closing of the connection. Transmission Control Protocol/Internet Protocol (TCP/IP) is the full set of standard protocols used on the Internet. Hypertext Transfer Protocol (HTTP) is an Internet protocol specifically for the World Wide Web. It provides a way for Web clients and servers to communicate primarily through the exchange of messages.

Multipurpose Internet Mail Extension (MIME) is a technique designed to insert attachments within individual e-mail files. MIME allows a Web server to deliver multiple forms of data to the user in a single transfer. Also, when creating a Web page, it could include text files as well as nontext files, such as sound, graphics, still images, and videos.

Intersection and Information Technology and Public Health. The applications of IT in public health are numerous and varied. One particularly

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