Flashcards
Database
Flashcards do conjunto (39)
- 1What are redundancies? Which consequences are involved with redundancies?=the multiple exitstence of value
-Data can be changed difficultly
-Data can be found difficultly - 2Discuss at least two different database models and describe two advantagesand disadvantages! (Object oriented database)Object-oriented database:
+manipulation of data happens by using methods
+data are seen as objects and saved as such (can be saved quickly and retrieved quickly and easily)
-hardly used
-missing standardization
-runtime behaviour not predictable - 3Discuss at least two different database models and describe two advantagesand disadvantages! (Hierarchic database)+data is saved in unique, sequential files
+first column indicates the hierarchic level, highest hierarchy has to be usefully assigned
-not flexible regarding changes in structure
-new data causes a huge copying process (delete operation only by using pointers, memory space for pointers need to be reserved after every data set) - 4Describe with your own words what a database is!consists of a collectino of data, which is stored in a computer!
- 5Write three points, which you requestfrom your database and explain them!-data has to be stored persistent. Storage has to be independent of runtime of programs or switch on- and off of computer
-there have to be any different search terms on the data pool(show address, how much entries..)
-database has to be designed for multi-user operation systemm which allows multiple users to access the single system - 6What ist he difference between a table and a relation?-every element can occur once in a relation
-no NULL values can occur in a relation
-the order is strictly defined within cross products, not whithin tables
-infinity of relations
-sorting options within tables - 7Mark attributes, attribute values, object, dataset, datasets, domain
- 8Describe in own word a dataset(tuple)!All characterisic values of an element complies with a dataset
- 9Describe in own word datasets(entity quantity)!All datasets of a table(entity) together create the entity quantity
- 10Describe in own word a domain(Range of values)!there are attributes where the possible attribute values have to be restricted.
This restrictions of values are called domain. - 11Describe in own word Null values!the null value does not comply with the number Null, but indicates that the attribute has no attribute value(important for key gving and analysis)
- 12Describe in own word objects(entity)!saved information represents persons.
A person complies to an object(entity) - 13Describe DBMS figure
- 14What is clustering?-takes care, that often requested data(which belong together), are stored physically next to each other
-aim: improving access speed on stored data - 15Explain the two clustering options!-Intra-File Clustering: persons, whose names lay alphabetically next to each other, would be stored side-by-side
-Inter-File Clustering: persons would be stored sorted by their city side-by-side(Information are stored in 2 separated tables) - 16A database is separated in three levels. Describe them in your own words.-Intern Level: physical storage
-Extern Level: different views, the end user has on the data
-Conceptual level: administrates the conncetion between intern and extern level - 17In which level do we find the data language. Explain why the data language can’t be in another level!->Extern Level
-cant appear in the intern level because the level only considers the physically storage
-in the conceptual level rules are established, so no data language is needed here - 18The data language contains two important parts. Which are they? Make for each part an example.-Data Definition Language(DDL):
only deals with the definition of the attributes and tables. For example the cration of a table with CREATE TABLE command.
-Data Manipulation Language(DML):
data sets are manipulated for example either by changing or inserting. For example, the import of data set due to an Inserts command. - 19We discussed about the „logical“ and „physical“ independence. Describe what is meant with it and tell me the advantages!The aim is that the user or the program dont recognize or are not affected by changes on the conceputal or intern levels
-operator: no source code adaption
-user: no training needed - 20Write at least three important tasks of a database administrator and describe them.-Design of conceptual level (conceptual schema, logical database design)
-design of intern level (internal schema, physical database design)
-user support (e.g. create, update, .. of database) - 21The DBMS has to cover several important areas! Describe at least one of themOptimization of manipulation instructions
to implement command optimal
DBMS is able to find optimal solution - 22Explain which level of a database is relational!-Conceptual Level works with tables and is relational
-Extern level can be relational but doesnt have to, depends on how the programing language looks at the data
-Intern level is not relational, because the storage type is defined - 23Explain in your own words what union–compatible/ type -compatible means and make an example!if two relations of one subset are included in the same cross product, this relation is also called union/type compatible
Example: R1= Persons from Dietzenbach
R2= Persons studying information technology - 24For which three operator is the type -compatibility required? Explain why?UNION , DIFFERENCE , INTERSECTION (Input are two symmetry classes and as output you get a new symmetry class)
- 25Which operators are at least needed for the relational database model?RESTRICT, PROJECT and JOIN
- 26Which advantages and disadvantages NULL values have?You don't always have a value ready. In such cases, no information can be entered; zero values must be treated separately for analyzes and selections.
- 27Name the eight operators1. JOIN, 2. UNION, 3. RESTRICT, 4. PROJECT, 5. PRODUCT, 6. DIVIDE, 7. INTERSECTION, 8. DIFFERENCE
- 28Which operator is used to restrict cross products?RESTRICT, building a subset
- 29Explain to me what is meant by a foreign key and tell me the reason why it plays an important role in referential integrity?A foreign key is just a placeholder. This refers to a value (which is a primary key) from another table.
-requires that each foreign key refers to a valid value
-to prevent actions that would destroy links between tables. - 30Explain to me the term primary key and tell me at least three important properties that a key should have (in addition there is the explanation of minimality)i) A primary key is an attribute or an attribute combination which must be unique for every single data set
(ii) Simple structure
(iii) if it is an attribute combination, it has to be as minimal as possible(irreducibility)
Minimal means if the primary key is no longer unique when an attribute is removed from an attribute combination, the primary key is minimal. - 31Can you describe what options are available to you for creating relationships? What are the advantages and disadvantages of this?i.RESTRICTED restricted: If you try to delete a data record that is referenced by a foreign key from another table, deletion is refused here.
ii.CASCADE: Here the delete command is passed on and all data records that refer to the data record to be deleted are passed on deleted.
CASCADE poses a risk during the deletion process, because unwanted deletion processes can no longer be undone. If you do not select RESTRICTED or CASCADE, RESTRICTED is automatically set. - 32Using an example, explain to me the.. a. ... non-trivial functional dependency (trivial = obvious) b. ... trivial functional dependency c. ... transitive dependencya.) ID -> A or {Surname, first name, type} -> {Geb. Date}
b.) {Name, first name, type} -> {First name} (You are looking for something you already know)
c.) [A-> b, b - /> a, b -> c] or (ID - > Place of birth-> type) means type transitive depending on ID - 33Explain to me in your own words the ... a. ...1. Normal form b. ... 2. Normal form c. ... 3. Normal forma. Atomic attributes, means the attribute must not contain several individual values. B. The first normal form must be fulfilled and all non-key attributes must not depend on one of the key candidates. C. transitive dependency must not exist (+1. and 2. normal form must be respected)
- 34Explain in your own words what a JOIN is.-combines columns from one or more tables in a relational database
- 35Cartesian product (Grad(RxS) and Card(RxS)).Grad(RxS) = Grad(R) + Grad(S) (#attributes)
Card(RxS) = Card(R) * Card(S) (#datasets) - 36Describe in your own words what is meant with candidate key? Which two important properties should a candidate key have?a set of attributes that uniquely identify tuples in a table
-Uniqueness(unique). Every element of [R] can clearly be characterized by the words of the attributes of K
-Irreducibility(minimalism). K loses the characteristic uniqueness as soon as one or several attributes out of K become removed - 37Describe two criteria’s for a „good“ Primary Key! Why do they have such a deep impact for us?-the Primary Key should be free from every user information (e.g.customer number)
-the Primary Key should have a simple structure (simple handling while programming) - 38Three characteristics of relational database model-structural aspect: data is regarded in table forumla
-manipulative aspect: data is provided to user in table formula. it can be manipulated that way. user in turn gets result in form of tables back
-data integrity: must be guaranteed - 39Please discuss in detailed the differences between EQUIJOIN, THETAJOIN and NATURAL JOIN.-EQUI =combines tables based on matching values in specified columns
-NATURAL =creates an implicit join clause for you based on the common columns in the two tables being joined
-THETA allows for arbitrary comparison relationships (such as ≥).
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- Descrição
- Fachabitur Informatik FlashCards sobre Database, criado por Chu Chu em 17-02-2021.
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- Chu Chu
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