[principles of database system] Chapter 4 advanced database model: Unified Modeling Language UML, object definition language ODL

4.7&4.8 Unified modeling language UML

Unified Modeling Language

UML and E/R The correspondence of the graph

UML	E/R Model
class	Entity set
relation	Binary connection
Association class	Contact properties
Subclass	isa level
Gather	Many to one contact
Combine	Many to one with referential integrity

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UML class And its key

• UML Classes and E/R The entity set in the model is similar .

• A class box is divided into three parts ：

  1. Top ： Class name
  2. middle ： attribute
  3. Bottom ： Method

• Specify primary key ： After each key attribute, add keyword PK

• example ：

  

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relation

• Definition ：

  Binary relationships between classes are called associations .

  （UML There is no multiple connection , A multiple connection is represented by multiple binary connections ）

• Associated representation ：

  In two UML Draw a line between classes , Mark the associated name below the line .

• Constraint on the number of objects ：

  There is a certain constraint on the number of connected objects in the Association class , This constraint is achieved by using a m..n The label indicates , At least m individual 、 at most n Objects are connected to objects at the other end .

  • m..* There is no upper limit
  • 0..* Indicates that there is no constraint on the number of objects
  • If there is no label , It's equivalent to 1..1 , Indicates that there is and only one .

• example ：

  

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• A representation of referential integrity

  See the book P102

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Self correlation

• Definition ：

  Both ends of an association can connect the same class , Such association is called self Association (self-association).

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• To distinguish the different roles of a class in self Association , Give each end of the association a name .

• Example ：

  

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Association class

• The Association class corresponds to E/R In the model , Contact properties

• Representation of associated classes ：

  Put it in the middle of the Correlation , Have your own name , Its attribute is the associated attribute it depends on .

• example ：

  

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Subclass

• Subclass key From the root level .

• In subclass , Only record those that are not in the parent class 【 Extra properties 】.

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• UML Allow a class to have 4 Different subclasses in ：

  • Complete to partial ：

    Each class C Whether the object of is a member of this subclass ？

    yes , Subclasses are complete ;

    Otherwise, it is incomplete .

  • Separate pairs of overlaps ：

    An object can appear in two subclasses , Subclasses overlap ;

    An object cannot be in two subclasses , Subclasses are separate .

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• Object oriented systems and E/R In the model The type limit of subclasses

  characteristic	Object oriented system	E/R Model
  Complete or partial ？	All allowed	All allowed
  Separate or overlap ？	Separate	Allow overlap

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• Representation of subclasses ：

  Point to the parent class with an empty triangle arrow .

  • example ：

    

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Aggregation and combination

• Gather

  • Definition ： Represents the many to one relationship between the class and the diamond end class ;

  • Express ：

    A line between two classes , The end is an empty diamond , Indicates that the label is 0..1

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• Combine

  • Definition ： Represents a many to one connection with referential integrity ;

  • Express ： The connection between two classes , The end is a solid black diamond , Indicates that the label is 1..1 >

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• Example ：

  

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UML Transformation from graph to relation

class -> Relationship

Create a relationship for each class , The relationship name is the class name , The attribute of the relationship is the attribute of the class .

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relation -> Relationship

• summary ： Key attributes of two connection classes + Association class （ If any ) Properties of

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• For each association, create a relationship with the name associated , The attribute of the relationship is the key attribute of the two connection classes ;
• If there is an associated class attached to the connection , Then the attributes of the relationship should include the attributes of the associated class .

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• example ：

  

  Movies (title, year, length, genre)

  Stars (name, address)

  Stars-in (movieTitle, movieYear, starName, salary, residuals)

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UML Subclass -> Relationship

• Three methods ：

  • E/R Method pattern （ The relationship of each subclass has only the key attribute and the subclass attribute ）

  • Object oriented methods （ Each entity is in a subclass relationship ）

  • Null value method （ All subclasses are represented by a relation ）

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• The choice of three methods ：

  • If Each layer is separate , use object-oriented ;

    And there is no need to consider every possible subtree , Because each object belongs to only one class and its ancestors .

  • If Each layer is both complete and separate . With object-oriented, you only need to build relationships for leaf nodes ;

  • If The layers are large and overlap on some or all layers , Then use E/R Method .

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Gather / Combine -> Relationship

• Aggregation and combination represent many to one associations , Don't build any relationships for them .

• Handle ：

  hold The key attribute of the class at the diamond end Add to Classes with non diamond ends in .

  about Gather , These attributes Can be null ;

  about Combine , These attributes Can't be empty .

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• example ：

  

  Transform into the following relationship pattern ：

  Studios (name, address)
  Movies (title, year, length, genre, studioName)
  MoviesExecs (cert#, name, address, networth)
  Presidents (cert#, studioName)

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Weak classes and support combinations -> Relationship

• Support combined annotation ：

  Use a letter “PK” As an anchor supporting composition , It means that the key attribute of the supporting class at the other end of the composition is part of the weak class key .

  • example ：

    

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• Transform the above example into a relational pattern ：

  Studios (name, address)

  Crews (number, crewChief, studioName)

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4.9&4.10 Object definition language ODL

Object Defination Language

ODL brief introduction

Class declaration

• key word class、 Class name 、 Class feature list .

  class <name> {
  	<list of properties>
  };
  
  

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attribute

• Statement ：attribute Attribute types Property name ;
• Attributes can be basic data types or complex types .

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contact

• Statement ：relationship type Contact name ;

• Contact type ：

  • For one more ： Class name

    relationship Studio ownedBy;
    

  • One to many 、 Many to many ： Collection types

    relationship Set<Start> stars;
    

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Reverse contact

• Reverse relationship They have to come in pairs .

• Definition （ Behind the corresponding connection ）：

  inverse  Class name :: Property name ;
  

• example ：

  

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The multiplicity of connections

ODL in , A pair of mutually opposite connections can be divided into many to one 、 One to one and many to many .

• Two contact statements corresponding to different types are used “Set<>”（ many ） and “ Type name ”（ One ） Different combinations of ;
• “ many ” It can be “ zero ”, Express “ Any subset （ Including empty sets ） All possible ”

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There are two classes C, D,

C, D The connection between	C The type of corresponding connection in	D in
Many to many	Set<D>	Set<C>
C To D It's many to one	D	Set<C>
D To C It's many to one	Set<D>	C
one-on-one	D	C

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ODL Data types in

• Basic types

  • Type of atom ： integer 、 floating-point 、 Character 、 String type 、 Boolean and enumerative .

  • Class name ： It is actually a structure that contains all the attributes and connections of the class .

• Structured model

  • Collection types

    • aggregate (set)：Set<T>, disorder 、 Elements cannot be repeated
    • package (bag)：Bag<T>, disorder 、 Elements can be repeated {1,2,1} and {2,1,1} It's the same package
    • list (list)：List<T>, The length can be 0、 Orderly .string namely list<char>.{1,2,1} and {2,1,1} It's a different list .

  • Array (array)：Array<T, i>, T Is an atomic type 、 Integers i Length .

    example ：Array<char,10>

  • Dictionaries (dictionary)：Dictionary<T, S>, Express T,S Finite set of element pairs .
    One T Corresponding to one S,T Is the only one. .

  • structure (structure) type
    if T1, …, Tn It's the type ,F1, …, Fn Their domain names ,

    be Struct N{T1 F1, …, Tn Fn} It's called N The type of structure , contain n Domains , Its first i Types are $T_i$, The domain name is $F_i$.

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• Contact type

  • It can be a class , Or apply to a collection of classes 、 Package or list type builder ;

  • Be careful ：

    Contact type cannot contain structure type 、 Type of atom . And cannot nest .

    The following three are corresponding The wrong sample ：

    Struct N {Movie field1, Star field2}
    Set<Integer>
    Set<Array<Star,10>>
    

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• Attribute types

  • It can be atomic type or other complex type ;
  • You can also use the type builder multiple times to build ;

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ODL Subclasses of

• The attributes of subclasses consist of ：

  Inherit all properties of the parent class , And their own attributes .

• Statement ：

  class C extends D
  

  Multiple inheritance , Separate categories with colons

  class C extends D : E
  

• example ：

  class CartoonMurderMystery extends Cartoon : MurderMystery {...};
  

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ODL Declaration of middle key

• Statement ： Use key perhaps keys（ Equivalent ）.

  • Single construction ：

    class C(keys(attr1, attr2)) {...}

  • Multiple keys ：

    class C (keys key1, key2, ...)

• Contact key

  When many to one connections are declared as keys , Indicates **“1” The end can be “ many ” End key **.

  • example

    See the book P113 example 4.54

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ODL -> Relationship

Overall approach ：

• ODL When the attribute in is of non atomic type ：

  • Nonatomic -> atom .

    Non atomic types are converted to atomic types in a specific way .

  • If there is an irregular relationship after transformation , According to Relational schema decomposition Method for optimization

ODL class -> Relationship

• Atomic attribute in class ：

  If all the features in the class are attributes 、 The types of attributes are all atomic types , Then directly transform .

  You can create an attribute to express the object identity and make it the key of the corresponding relationship （ Such as id value ）.

  example ：

  

  MovieExecs (cert#, name, address, networth)

• Non atomic attribute in class ：

  • Structure type

    Define a relationship attribute for each field of the structure , Rename if naming conflicts .

    example ：
    

  • Collection types

    For the properties A Set of values for , Construct a tuple for each value in the set , The tuple includes attributes A And the corresponding values of all other attributes in the class .

    But there may be irregular relationships （ General violation BCNF）, At this time, use the decomposition method to eliminate the exception .

  • Other types

    • package ： increase count Attribute records the number of occurrences of each tuple in the package .

      

    • list ： increase position Property indicates the location of the corresponding address in the list .

      

    • Fixed length array

      

    • Dictionaries ： Expressed as a set of two tuples composed of key fields and value fields .

      

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ODL contact -> Relationship

• stay ODL in , Relationships appear in pairs opposite to each other ;

  For each pair of contacts , Just build a relationship .

• Be careful ：

  • Yes “ For one more ” contact , Connect this contact with In touch “ many ” On the other side of Class to establish a relationship （ That is, two relationships with common keys are combined ）, Will not destroy BCNF Conditions .
  • Many to one connections cannot be combined “ One ” Fang , Will violate BCNF Conditions .
  • Many to many connections cannot be combined .