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dbFull

Shez F Inglés 115 fichas

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  1. 1What Does A Relational Database ContainContains multiple tables of data that relate to each other using special key fields
  2. 2Problem with having multiple files1- Old code has no knowledge of new file
    2 - Danger of data duplications
  3. 3Databases need to abstract over 3 thingsData Structure
    Data Access
    Data Values
  4. 4What Does DBMS Do?Abstract Over the Database
    Restricts unauthorized access
    Enforces integrity constraints
  5. 5What are the Layers in DBMS and explain each oneLogical Layer: The view output to the user
    Physical Layer: How data is stored
  6. 6What is Data IndependenceOrganize and re-organize the structure of data
  7. 7What is data abstraction1- Conceptual representation of data
    2 - Database provide abstraction through independence
    3 - Uses logical concepts Such as Objects, Attributes and relationships
  8. 8What does the System Catalog containData Definitions
    Store Structure
    Constraints
  9. 9Define Views (not the drake album lmao)Present different views of data to different actors
    You have to centralize the data to show what each application needs. Hide the rest
  10. 10What is virtual viewsThis isn't stored
    No wasted space
  11. 11What is Concurrent Access in DBMSFeature of DBMS
    Systems using this are called OLTP
    Online transaction processing systems
  12. 12Define an Entity, Attribute, RelationshipEntity - Thing
    Attribute - Describing the thing
    Relationships - associations among entities
  13. 13Define a Record and a SchemaRecord - Underlying data aggregation
    Schema - Defines the types of values as they are entered
  14. 14What is a Relational ModelMathematical style for information
  15. 15What is a Relation and explain a row, column1 - Table of values is a relation
    2 - A row is a tuple
    3 - Column
  16. 16What is the Domain1 - Set of atomic values
    2 - Denoted as Dom(TABLE_NAME) = (ATTRB < 3)
    3 - Has a data type attached to it
  17. 17RelationsRelations denoted by R(A1, A2)
    R = Relation A = Attribute
  18. 18DegreeThe number of attributes a relation has. So if R(A1, A2), has a degree of 2
  19. 19What is a Tuple1 - A Row
    2 - Ordering of the tuples doesnt matter
    3 - Ordering of the columns does matter
  20. 20Define a Super KeySet of One or more attributes that guarantees uniqueness
    Super key identifies a unique tuple
  21. 21What is a Candidate KeyAny Key which can be a primary key
  22. 22What is a Primary KeyHas to be a subset of a candidate key
    Cannot be null
    Attributes are underlined
    Uniquely identifies a tuple
  23. 23What is a Foreign KeyEnsures Referential Integrity
    A tuple in one relation refers to another tuple in another relation
  24. 24Relational AlgebraLanguage to describe operations in a relational DBMS
    When we query a relation, has to be unique records returned
  25. 25SELECT (RELATIONAL ALGEBRA)1 - Denoted by Sigma
    2 - Selects a subset from relation based on operation
  26. 26Commutative DefinitionDoesn't matter which order
  27. 27PROJECT (RELATIONAL ALGEBRA)1 - Denoted by Pi
    2 - Not Commutative
    3 - Eliminates Duplicates
  28. 28RENAME (RELATIONAL ALGEBRA)1 - Denoted by Rho
    2 - Change the name of an attribute that we want to change
  29. 29What is a Union1 - Denoted by U
    2 - Joins 2 tuples together
    3 - Eliminates duplicates
    4 - Can be unordered
  30. 30What is an Intersection1 - Denoted by n
    2 - gets the result of records which are common in both
  31. 31What is the "Difference"1 - Denoted by -
    2 - R - S
    3 - Whats in R that isn't in S
  32. 32Tijan Product1 - Denoted by X
    2 - All combinations of tuples
  33. 33What is a Join1 - Denoted By |X|
    2 - Combining tuples from 2 relations into a single tuple
    3 - No duplicates
    4 - Removes redundant data
  34. 34Equi-Join1 - performs a JOIN against equality or matching column(s) values of the associated tables
  35. 35Natural Join1 - Is a type of Equi Join and is structured in such a way that, columns with the same name of associated tables will appear once only.
  36. 36Name Some Aggregate Functions and explain each oneCOUNT - Returns the number of rows satisfying the criteria
    AVG - calculates the average value of a column of numeric type
    SUM - returns the sum of all selected column.
  37. 37Explain Left and Right Outer JoinsLeft Outer Join - ]X|
    1 - Retains all record on the left
    Right Outer Join - |X[
    1 - retains all record from the right
  38. 38Explain what is an Outer Join and A Full OuterOuter Join - when a join is done, matching tuples are used, the rest is thrown away, outer joins retains these records
    Full outer - ]X[
    1 - retains all the records from both tables
  39. 39Define and explain the Schema1 - Roadmap of data to be stored
    2 - Allows user to declare types of record required
    3 - declares relationship among entities
  40. 40Name All the Levels of the Schema1 - Internal
    2 - Conceptual
    3 - External
  41. 41Explain The Internal Schema1 - Defines database as collection of logical records
    2 - Internal name of fields and the number of bytes they occupy
  42. 42Explain the Conceptual Level Of Schema1 - Hides detail of storage
    2 - focuses on entities, attributes, relationships
  43. 43Explain the External Level Of Schema1 - Hides the rest of the database to the user if they are not allowed to see it
  44. 44What is Physical Data Independence1 - To change the Internal Schema Level without having to change anything from the conceptual and external level
  45. 45What is Logical Data Independence1 - Capacity to change the conceptual schema
    2 - if we remove an attribute that we are using, we have to change the view table
  46. 46What is NormalizationTakes the schema through steps to see if it satisfies a certain form
  47. 47Name the forms in the scope of SCC 2011NF
    2NF
    3NF
    BCNF
  48. 48What does a database have to be to satisfy 1NF1 - No Multi valued attributes
    2 - Must be a single value for each attribute
    3 - domain of an attribute must have atomic values
  49. 49What are the Techniques to Ensure 1NFPrimary Key Propagation
    Tuple Expansion
    Expand Attributes
  50. 50Primary Key Propagation1 - Remove the multi valued attribute which is not satisfying 1NF, and take the primary key of that relation and create a new table
    EG - If Location has multi valued attribute, then take the primary key of that relation eg ID and make a new table called Locations with ID as the Pkey
  51. 51How do I expand the tuple1 - Expanding the tuples so that each location is split into singular tuples.
    2 - This can cause redundancy
  52. 52Expand the Attributes1 - If there is an attribute called marks which has Dom(Marks){1,2,3,4,5}
    2 - Then you would have to make extra attribute headers with M1 ... M5 to accommodate this
    3 - Can have null values
  53. 53How To Make Sure Database is in 2NF1 - You are confident in 1NF
    2 - Every Non Prime Attribute is fully functionally dependent on the primary key of R
  54. 54What are Prime and Non Prime AttributesPrime - Attribute which is part of a key
    Non Prime - Attribute which is not part of a key
  55. 55What are the different types of dependencies in 2NF1 - Functional
    2 - Fully Functional
    3 - Partial
  56. 56What is Functional Dependency with an example1 - When given attribute A, will always get attribute B
    2 - A -> B
  57. 57What is Fully Functional Dependency with an example2 - A combination of attributes will always provide a result for another
    AB -> C
  58. 58What is Partial Dependency with an example1 - When an attribute is dependent on part of a key. If AB = Keys
    B -> C
    2 - C is partially dependent on B which is part of a key
  59. 59Explain how my Database can be in 3NF1 - You have to be confident in 1NF and 2NF
    2 - No non prime attributes is transitive dependent on any key
  60. 60Define A transitive dependency with an example1 - Transitive dependency is where a non prime attribute is dependent on another non prime attribute
    A = key
    A -> B
    B -> C
  61. 61ER Model1 - Graphical Representation of the database structure
    2 - Allows analysis, specification and design of the structure of the database
  62. 62What are Entities in ER Model1 - Data about a specific object
    2 - Graphical Notation of a rectangle
  63. 63What are Relationships in the ER Model1 - Associations among entities
    2 - Graphical notation of a diamond lmao
    3 - Entity Relationship Entity
  64. 64Degrees of a RelationshipNumber of participating entity types
  65. 65Recursive RelationshipIs where the participating entity is the same
    Person Marries Person
    Person Sex Person
    Alex Shoot Child who is called Alex
  66. 66Cardinality Relationships1:1 which means a person can be married to only one person
    1:M means a person can be married to many people
    M:N means many people can be married to many people
    EG
    Department - 1 - ENROLS - N - Student
  67. 67Attributes1 - Properties describing an entity
    2 - Graphical notation of speech bubble
  68. 68Key Attributes1 - Have unique values for each entity type
    2 - Need to Underline this attribute
  69. 69Atomic Attributes1 - Attributes that you cannot break down
  70. 70Composite Attribute1 - Attirubtes which can be divided into other attributes
    2 - Name can be divided into FName and LName
    3 - Graphical notation is speech bubbles coming from attributes
    Name will have 2 speech bubbles, with FName and LName
  71. 71Single Valued Attribute1 - Have a single value for a particular instance of entity type
    2 - Single values of the same type
  72. 72Multi-Valued Attribute1 - Multiple values for an attribute
    2 - Graphical notation for this is the 2 lined speech bubble
  73. 73ER To Relational1 - Like Normalisation
    2 - Step by step
    3 - Check each step and dont do multiple steps at once
  74. 74ER To Relational Step 11 - Find the simple attributes - things we're interested in
    2 - ignore multi valued attribute
    3 - figure out key attributes and form table out of these
  75. 75ER To Relational Step 21 - Find 1:1 Relationships of 2 Relations
    2 - Include primary key of one as foreign key of another
    EG: S and T
    - inlcude primary key of T as Foreign Key of S
  76. 76ER To Relational Step 31 - Find 1:N Relationships
    2 - Use the 1 as the Foreign key to N
  77. 77ER To Relational Step 41 - Find M:N Relationships
    2 - Create a table which takes the key values from both M and N.
  78. 78ER To Relational Step 51 - Look at each multi valued attribute and create a new Relation R
    2 - Include the primary key of the relation which has the multi valued attribute as well as the multi valued attribute itself. This will be a foreign key
    3 -
  79. 79Physical Secondary Storage Devices1 - Magnetic Disks
    2 - Too large to fit into main memory
    3 - cost of storage is high for data
  80. 80Techniques of StorageDatabase is organized on disk into files of records
  81. 81Define a Record1 - A form for storing data
    2 - Includes, values, types, record type
  82. 82Binary Large ObjectsLarge unstructured objects that represent images, video, audio
    Stored separately from its record in a pool of disk blocks
  83. 83What is a File1 - Sequence of records
  84. 84Fixed Length RecordsEvery record in file has exactly same size in bytes
  85. 85Variable Length Records1 - Look at the maximum length a variable can take
  86. 86Variable Length Fields1 - Can be terminated by special seperator character
  87. 87Record Blocking1 - Records of file must be allocated to disk blocks
    2 - A block may contain several records
    3 - A block may contain only part of a record
  88. 88Spanned RecordsStore part of record in unused space with pointer to block containing remainder
  89. 89UnSpanned RecordsRecords are not allowed to cross block boundaries
    May get blocks with too less to or too much
  90. 90What is Continuous Allocation and +Ve and -Ve1 - Blocks are allocated to consecutive disk blocks
    2 - +ve - very fast reading of whole file
    3 - -ve - file expansion is difficult
  91. 91What is Linked Allocation and +Ve and -Ve1 - Each file block contains a pointer to next file block
    2 - +Ve - file expansion is easy
    3 - -Ve - very slow reading of file
  92. 92What is Clustering IndexAllocate clusters of consecutive disk blocks and link the clusters
  93. 93What is Indexed Allocation and +Ve of it1 - One or more index blocks contain pointers to actual file blocks
    2 - +Ve speeds up access to records partway through file
  94. 94What is a File Header1 - Known as a file descriptor
    2 - Contains information in file
    3 - Determines disk address
  95. 95Primary File OrganisationHow records of a file are physically placed on a disk
  96. 96Secondary File OrganisationEfficient access to records of a file based on fields
  97. 97What are Files with Unordered Records1 - Called heap files
    2 - Simple and basic type of organisation
    3 - Records are placed in file in order they are inserted
  98. 98+Ve -Ve of Files with Unordered Records1 - Insertion is very efficient
    2 - Deletion is expensive
  99. 99Files of Ordered RecordsPhysically order records of a file based on value of fields
  100. 100+Ve and -Ve or Ordered Records1 - Reading records is efficient
    2 - Insertion and Deletion is expensive
  101. 101What are Secondary Files1 - We have access structures called Indexes
    2 - Used to speed of up retrieval of records
  102. 102What are the Types of Single Level Index On Ordered FilesPrimary Index
    Secondary Index
    Clustering Index
  103. 103What is a Primary Index1 - Specified on ordering key field of an Ordered File
  104. 104-Ve Of Primary Index1 - Insertion and Deletion is a Problem Could use a deletion marker
  105. 105What is a Clustering Index1 - Used if Ordering field is a non-key field
    2 - Defined on an ordered file
  106. 106-Ve Of Clustering IndexInsertion And Deletion again...
  107. 107What is a Secondary Index1 - Specified on any non ordering field of a file
    2 - Records not ordered by values
    3 - Secondary Index is ordered
  108. 108In a Tree Structure what is Level 0 CalledRoot
  109. 109What Is A Search Tree1 - Used to search for a record given its value
  110. 110What is meant by "P" in terms of TreeP = Number of pointer each node has
    The number of values each node has is usually p-1
  111. 111What is meant by a "Balanced" TreeAll nodes have to be at the same level
  112. 112What is a Leaf Node1 - Nodes which have no pointers
  113. 113What is a B(-) Tree1 - Type of Search Tree
    2 - Needs to be a balanced tree
  114. 114Insertion of a B(-) Tree1 - Take a number and insert into node
    2 - If node is full, take the middle value and push it up
  115. 115Deletion of a B(-) Tree1 - If deleting causes node to be less than half full
    2 - Borrow from left if Full else merge
    3 - Borrow from right if Full else merge

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Fichas sobre dbFull, creado por Shez F el 28/04/2017.
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Shez F
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