Data structures

Whenever we enter data into a computer, we have to be able to talk about the data we are entering. To do this easily, we must define the words used to describe that data. Let's take an example.

Let's say that we want to enter people's names and addresses into a computer so that we can have the computer print some mailing labels⁵ for us. The first person we are entering has as his address "1234 Apple St.". There are several ways we could enter this data. One way would be to enter the house number by typing the digits "I", "2", "3", "4" on the computer. Then we might press the space bar⁶ to put a space between the address number arid the street name. Then we could type the letters "A", "p", "p", "I", "e" and then the space bar again to put a space between the "Apple" and the street designation, the abbreviation "St." Each time that we press a key on the keyboard, we enter what is called a character into the computer.

' to spot an error - обнаружить ошибку

² is the case with the computer test data—возникает в связи с компьютерными .тестовыми (контрольными) данными

³ Last but not least — Последнее по порядку, но не по важности

⁴ on a regular basis -- систематически

⁵ mailing label — почтовый адрес ^h space har — клавиша пробела

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Figure 5. A mailing label. The "G" in "George" is called a character. A logical group of characters such as "Anyplace" is cailed a field. in this case an address field. A logical group of fields (Name, Address, City, and Zip Code') is called a record. If we had 100 de­ferent mailing labels similar to the one shown above, each label would be a person's record.

Characters

A character can be any key on a computer keyboard. That key may or may not result in something being printed. The digits "1 2 3 4" are all printing characters, but when we hit the space bar, we entered a character which indicated we wanted one space, either between the digits or between the house number and the street name. This character, the space character, did not print; it is an example of a non-printing character. Most of the control characters,² as well as the escape key,³ the tab key,⁴ the return key, the line-feed key,⁶ and the space bar generate what we call non-printing characters.

Fields

A group of many characters make up what is called a field. A field is any arbitrary but logical group of characters. For example, 1234 Apple St. could be entered alt as one field, which we might call the address field, or we could have our choice of entering this data as either two or three fields. If we entered the address as two fields, we could have a house number field and a street name field, in which case the house number (1234) would

Zip Code == Zone Improvement Program Code—почтовый индекс

control character—управляющий символ

escape key ~ клавиша перехода (с одного кода, языка, регистра на другой)

tab key—клавиша метки табуляции

return key—-клавиша возврата

line-feed key—клавиша перевода строки

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be entered into the house number field, and the street name (Apple St.) would be entered into the street name field. If we so desired, we could enter the data into three fields, with the house number entered into the house number field, the street name into the street name field, and a street type entered into the street type field, which could contain such abbreviations as "St.", "Ave.", "Blvd.", and "Rd.".

The decision to group data within specific fields depends on how the data is to be accessed. The computer system treats the data in any field as a unit. Choosing to have an address field implies that we want to treat the address "1234 Apple St." as a unit. Sepa­rating the data into a house number field and a street name field lets us process the house number portion of the address apart from the street name portion.¹ Thus, separating the data into fields helps organize the data for processing,

For each person we wanted to enter into the computer, using that person's full name and address, we would enter many charac­ters. A group of characters would fall into a field and many fields would come together to form a single person's mailing label. We could have a' last name³ field, a first name³ field, and a middle name⁴ field. Then we could set up a house number field, a street name field, and a street type field. To complete the address, we need a city name field, a state field, maybe a country field, and certainly a zip code field. A field, then, is a group of characters that have something in common; the last name field wilt-contain a group of characters that combine to spell out a person's last name.

Records

If we were to enter the names and addresses of a hundred different people, so that the computer would generate a hundred different mafling labels, we would be entering a hundred records into the computer. Each record is made up of many fields, just as each field is made up of many characters.

Files

When we finally gathered all of the records representing the total information necessary for all of the mailing labels, we would store these together in the computer in what is called a file.

' lets us process the house number portion of the address apart from the street

name portion — позволяет нам обрабатывать часть адреса “номер дома”

отдельно от части “название улицы”

^г last name—фамилия (например. Smith в полном имени John Smith.) '' first name—собственно имя (например, John в полном имени John Smith,! ⁴ middle пате—второе имя (например. May а полном имени Louise May

Smilh}

Let's think of it another way. Take the common office term "file", which means a group of pieces of paper that are put to­gether into a jacket or envelope and placed together on a file shelf. If we wanted to keep the names and addresses of all of our customers in one location, we could have several sheets of paper, one sheet for each customer, placed into a file folder.' The office file folder corresponds to the data processing file. Each file folder contains many pieces of paper, with one customer's name and address on each piece (the individual pieces of paper correspond to records).

Each piece of paper could be a form made up of boxes, and in each box we could put the person's name, address, city, state, or whatever information was called for on the form. In data process­ing, the equivalent of each long box that is filled in on the form is the field. Each letter that we use to fill in the box is a character. Picture the file folder with letters on a piece of paper and many letters and numbers (characters) grouped together in a box (field) to make up a person's name and address. Many boxes are put together to make the form, or record. All of these forms are put into an envelope called a file folder — in data processing terms, a file.

Volume

A whole group of data processing files can be put together in what is called a volume, and stored on a reel of magnetic storage tape.² In our office analogy, a volume would equal a whole file shelf, each shelf containing many file folders.

Library

A collection of magnetic tapes put together is called a library, just as a whole group of filing cabinet shelves is called a filing system.

It is essential to become familiar with³ the common data pro­cessing terms:

character—each key that is entered on the keyboard;

field — a group of characters, such as person's last name;

record— all of the information about one person;

file — a group of all of the records that we want to keep together.

A number of files of a company's customers go on to a volume, and many volumes make up a library.

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file folder — папка-скоросшиватель ^ magnetic storage tape—магнитная лента-накопитель to become familiar with — усвоить

² Зяк. 3161) Л Л. Bfiuc