Hi!!! I am writing because although you said to the other Blanca that write you a email with her exactly direction for the block we have not your email adresse it is for that I am going to put here her adresse: I hope everything will be ok!!
Blanca.DelCastillo.Uni-linz and /blanka.
Thanks very much for all.

Thats the last class.
At the beginning we were spoken about other themes for other days and after that we have to do every student a question that we had about something of the study.
And that is what we were talking about:

3.3.2.Relationale Bank.

3.3.2.1.Daten modelling.

If a relational database to be built, it is first of all a conceptual model that the users of application programs or data required describes developed.

One commonly used method of data modelling is the entity-relationship - model. Through entity relations relationship map, the object classes by rechecked, the relationships between the property by diamond type attribute necessary by the oval. Primary keys are underlined. In dependence of them, as many - to - many - relationships. Relationships can also attribute to have.

3.3.2.2. The business model.

The diagram is a simple business model an instructive book a commercial basis. The "customers" issue repeatedly "sluggish" to the teaching buch handel. Each "contract" can have several "books", each in any quantity ordered. Several "publishers" embarrassed "books" with a "book" with a certain number and title only of a "publishing house" can come as a certain "order" exactly one "customer" is assigned.

3.3.2.3. ER elements.

For graphical representation of the model he has presented ungs following elements:
A lot entiltäts than rectangle. In the book action there is the example entitäts volume customer. On contract. Paper and publishing. As entität be distinct objects from the world. These can be tangible or abstract nature.

An attribute is used as ellipse or district represents. In the book action - as the example has to contribute to attribute No, no release date customers.
Attributes (properties) risieren a entität characters or a relationship (see the relationship between the contribution and to book the amount of property. Order is made, how many exemplares a Paper in a contract to be ordered)

A key or primary key is in red.
Key used for sorting, searching and finding in databases. If an entity not appropriate key, can be added to artificial keys, such as a number. A primary key allows for the identification of any entity. It must be unique. So some may not two different customers the same customer number.

Relations between entities as diamonds drawn. In the diamond, the name of the relationship. To secure it, the reality derived from concepts to choose. A relationship volume is a collection of links to the same kind of linkage entity levels.
1:1 - Relationship: There can be only one element of an entity with one element from another entity connected.
1: n Relationship: An item from an entity with several other elements of a combined entity, but not vice versa.
N: m relationships: Any number of elements of an entity can use any number of other elements of a combined entity.
Special cases:
Part of relationship. In cases of aggregation. Should such collective works in a database abgbildet, so, for example, part of volumes.
Is-a relationship press a specialization or generalization. Example can entity quantities themselves in a lot merged entity. For example, "French textbooks" specialization of the entity quantity "language books."

3.3.2.4. Defining the relations (tables)

The presentation of the need in a facility Let ER diagram, with their relationships and attributes does not lead directly to the tables of a relational database. To deduce the corresponding tables are building for the tables to be observed, particularly in the so-called. Normal forms are combined.
A table is a collection of data on a given topic. If you have a theme for each separate table, avoiding duplicate data. The backup will be more efficient, and error in the input will be reduced.
In tables are data in columns (fields), and rows (records). Each field in the table seben book contains the information for each book.
There are 4 conditions on a table:
-- A table must be unique. This means that at no time two identical records in the table must exist. It contains only one record.
-- A table must atomic attributes and domains.
-- The records are at all times as unsorted.
-- The attribute sequence is never firmly defined.

The following operations are possible with tables:
-- A (blank) Data Set
-- A data (rate) search
-- Data fields
-- Delete a record
-- (Attributes add / delete)


3.3.2.5. Normalizing the tables

With the transfer of the object classes in these tables are then to examine whether they dependencies of the fields themselves. Normalizes, by progressively reviewed whether the tables formed in conditions of normal forms. During this normalization process comes to a reduction of redundancy, but also in parallel to an increase in the number of tables. Whenever discover redundancies will lead to the formation of new tables, through the key fields combined. The adaptation of the tables, on the key fields combined. The adaptation of the tables to the normal forms is the basis of SQL.

1. Normal Form: Remove Repetition group

Each field in the data set may be unique. There are several areas of the same type, they must own them in a relationship be saved.
The transfer of the object class "contract" in a table (relation), the verbal description of the business model accordingly "Each job may contain a number of books, each in any quantity ordered."
As a rule of order in several different books in different amounts, the fields: "Postionsnummer" and "quantity" several times before, was 1 Normal form objects.
The consequence is therefore outsourcing of repeat gruop in a separate table “Auftragspos" and the combination of the tables on the key fields.
The field "no" on the table "mandate" is key field of the table "contract" and is therefore compatible with the box “Auftragspos”. Order number". The names of the two fields differ, but the content is in both cases ident Here is an inevitable redundancy un relational databases, which are also controlled by redundancy and redundancy of not talking.
For the fulfillment of the business model described tasks sin detailed data about the books required.

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.

Hello!
As I said in the story of my Holidays, the days here are now not too fun, we have to study, it is cold, we have eaten to much during the Holidays and now we want to eat less...;)

But it is not all so, because last Saturday we went to Dachstein to ski!!
I can´t skiing very well, the truth is that I do it really bad because I have been skiyng only two times in my life in Spain, in a city near Sevilla whis is called Granada.But it does not matter, we went there a great group and we spent there the day and it was really good!!
Here are some photos!!