3.3 Databases


A function of a computer system is, data, text, images, language, sounds store, so that their needs, particularly swift and easy retrieval and benefits possible.
For the user of a personal computer is often the situation on that information will be evaluated and processed, for example, in several different graphics, reports and spreadsheets are included. These documents are often using different software packages such as different file formats. The retrieval, and above all, the benefit of these documents therefore requires knowledge of each set PC file formats.
In this section, in particular, is a matter of how large volumes of data reliably and permanently stored and retrieved when needed them. Therefore it is necessary for one or more users relevant Ausschitte from reality isolate, and the latter in conventional file systems or databases way. Basic questions of the data organization and the planning of database systems and tools for the widespread use of databases are therefore more content this section.

3.3.1. From the file to the database

Files, and therefore those databases contain illustrations of the reality that for inter-operational and information and communication processes as necessary as, for example, prove useful. The completeness and accuracy, for example, a file or database can only involvement in the real environment assessed.

3.3.1.1. The objects file and sentence

A set is an object of simplistic reality in a computer system. One such object can be a concrete object, an event or an abstract concept. It is described by its attributes. The object "textbook" can be, for example, by the attributes "number", "Author", "title", "price", "Publishing" and "stock" to describe. The concrete contents of the specific attributes of a textbook will be assigned fields. All fields of a specific object constitute a record. A tabular presentation is suitable for excellent. The table can be to the description of other objects to be extended.
Data fields are the smallest unit of files and databases. Data fields are marked with a name, following often with the name of the attributes and can cover different date types. The fields "number" and "there" are like Type, "integer", the field "price" of the type "decimal number." The fields "author", "title" and "publishers" are of the type "text" and the "leaking" of the type "flag" (with the expression "y" or "n").

From similar deresn attribute objects and object classes are formed. A file is a great property; they consist of one or more date rates. In that field, or those areas in which a artefacts. Key are assembled from several fields, they are as combinations key.

Such structured files are sometimes referred to as flat, classic or conventional files. Bezuges because of the heavy tasks of services to meet individual user files in the conventional rule is not the inner - and inter-task diversity. A major lack of organisation means of data files is occurring redundancy and inconsistence within the file and other files za, the company will be led.


Characteristic of conventional files is also the strong, mutual dependence with the application accessing these programmes. Advances operational procedures, and legal or other changes often make adjustments in the structure of datein necessary. It must, for example, New fields added to a file. In the above example "lehrb <úcher" could be a change in the order - and lieferungs process (of the logistics) the file extension of the "book" to the field "isbn" require



3.3.1.2. Use of a conventional file

Based on the following examples are depicted in simple query calculation tables tools explained. Does the program will feature "special filter".
The process of a file from those records filters, which meet the specified criteria, the selection means. The basis of selection is the use of logical operators (and, or, not), comparison operators (equal, not equal, bigger, smaller, More immediately, small equal) arithmetic operators and special operators. If, however, from the present number of data fields only certain selected, it is called projection. Selection and projection can be executed in parallel.

3.3.1.3. DBMS database systems (management)

Database systems are characterized by the fact that by several / many users and applications used data in a global model (conceptual model).
There is a decoupling of the problems of data storage and data organization of the technical tasks of the users. Redundancies are only for reasons of security, integrity or faster access time tolerated. Inconsistencies will, as far as possible off.
Database systems are made up of the database and a DBMS. It should basically be whether the data model hierarchy, the network model or the most widely used, explained below relational model is based.



All that is the theory about we have been talking at class today and we have been learned with an example how to differenciate between specialfilter and standfilter in a database.
We have learned it by an example with books.
The special filters have not to be complex and have to be exposed to logic for the relationship to be meaningful and the computer will understand.
For example said: search chemistry books published by the company "X", that the computer understands it is only "A and B" for example.
Examples of criteria for filtering are "A and B" and "A or B" simple, not complex.All this is not what is known as "selection".
We have also seen that there is a database, the area where establishing criteria and the result area, all these fields we have seen directly on the computer with the example we have been doing in class, and thus the entire theory has been previously explained more clearly.

3.2.4. Selected functions for business purposes.


3.2.4.1. Overview of the functions.

The following overview shows, which currently features usually in tables kalkulations programs are available, although in particular. In the subsequent detaillierung those selected were required for the solution of tasks of business relevance. Current tables kalkulations programs regularly offer a multiple of functions in the various areas; they should because of the examples here learned in demand also falls under these additional functions out tion of the help function.

Financial Mathematical Functions:

= Bw. ......... Bart returns the value of an investment.
= IKV ......... Internet equity interest rates.
= LIA ......... Linear depreciation rate.
= Etc

Date Functions:

= Date ....... reckons with the day, month, year una specified date in order enine current number, you can then sangaben date.
= Today ....... returns the current date.
= Year ........ calculated from the number dder current year.
= Etc

Information functions:

= Istfehler .... returns true if the cell contains an error value, it can also query whether a cell respect (istbezug), a re except (istfehl), a text (isttext), not text (istktext) , a blank cell (istleer), a truth swert (istlog), a fehlerwert (istnv) or a number (istzahl).
Typ = ......... provides a number of the datentyp the specified value.
= Cell ....... provides information about formatting, position or content of a cell.

Mathematical and trigonometric functions:

= ABS ...... OrderForm absolutwet as a result of the number.
= ARCCOS delivers the Arkuscosinus ....
= ARCSIN delivers the arkussinus ....
= Etc.

Statistical Functions :

= NUMBER ... as a result provides the number of pay.
= ANZAHL2 .. as a result provides the number of pay, any values.
= MAX ...... supplies grisste number from the argumentliste.

Matrix functions:

= MDET ..... determinante provides a matrix.
= MINV ..... returns the inverse of a matrix.
= MMULT .... delivers the matrizen produckt.
= Etc



Text functions:

= PARTY ..... converts a number with a fixed number of comma, in a text.
= FIND ... looking for a text in a text and gives the position ¨. Large / small description will beahtet.
= GROSS .... Waldelt text in big letters.

Logical Functions :

= FALSE .... as a result provides the (wahrheits) worth wrong.
= NOT ..... returns TRUE, if the argument was false, and vice versa.
= TRUE ...... provides the true heitswert TRUE

3.2.4.3. Statische functions

The most commonly used formula is certainly the sum formula. It was therefore Excel 3.0 as a separate icon in the toolbar and click of a button can be entered.

The function returns expected, the sum total of the figures cited as arguments. In some programs, this function is designed to provide only a range argument can edit. Therefore, the formula in cell is not defined anywhere.

Figures is either a single number or a range of numbers. It can be fixed values, formulas or references to other cells can be entered. If the specified range references to cells, which do not contain figures, they are simply disregarded. Would these cells by adding operators added, it would be the result of the error value, because not all cells addiebare values.

Be texts or truth-values directly as arguments in the sum formula, then they are converted into numbers and very probably counted. TRUE will be counted as number 1, text with the appropriate numeric value. Do arguments, which are not convertible in numbers are directly as an argument in the sum formula, then the error value # VALUE.

The function NUMBER notes how many numbers in the Argumentlische contained and returns the appropriate value. Only values, the null, numbers, truth-values, datumsangaben or numbers in text form sind.Fehlerwerte be counted just like text, which is not convertible into figures. Do you want to include all cells, which contain anything, it stands for the function ANZAHL2 available. These include all cells, which are not empty. Cells with empty text is not empty.

The AVERAGE aritmetische provides the means of defined figures. Blank fields are not upošteva, fields with 0 on the other hand, already, even if they do not appear.

The function ABUNDANCE is in a class division over a range of numbers. For example, the data in Figure 3.2 / 8 in five categories, with a clef.
It can use this function automatically creates a frequency distribution of the individual notes, which now has been a rather cumbersome combination of database and multi-operation could be achieved.

The MODALWERT delivers the most value of a data series. With SCHIEFE the skewness of the distribution. The curvature of the distribution compared with a normal distribution is determined by the Kurtosis describe what the function KURT Excel offers.

To those Populations know sizes for a given number of group to be able to quickly determine, there is the command in Excel "analysis functions" In the pull-down menu "Tools". Using this feature allows for a range of cells as comfortable histograms, moving average, rank and quartile, and the drawing of samples carried out.



3.2.4.4. Logische functions

The spreadsheet can no defined processes, as it is not procedurally is built. However, many situations in which, according to a different value, a cell one, or a different value. It is not possible with functions, depending on one condition a value in one or another cell Submitted. But it is quite possible, in a cell, depending on one condition, different values represent. This objective serves the function if:
The truth-value can be used either directly in a cell, then to be referred, or it is the result of a comparison operation.
It often happens that several conditions linked. To serve both AND and OR functions.
The OR function returns true if at least one condition is TRUE, and the function returns the result TRUE if all conditions contained therein are true. With the result is not reversed.

3.2.4.5. Date functions

With the functions DAY, MONTH, YEAR, HOUR, SECOND MINUTE, and the individual values from the serial number. The integer part represents the date, the decimal time. The WEEKDAY function, which is also the current number is used as an argument, returns a number between 1 and 7
Important: The Mac operating system calculates the date generally from 1.1.1904, while Windows default with the 1.1.1900 begins. One must in the Windows version of Excel is the option date values from 1904 to take the same calculation basis.