index.md (6020B)
1 +++ 2 title = 'Structure modeling with UML' 3 +++ 4 ## Structure modeling with UML 5 6 ### Class 7 8 a construction plan for a set of similar objects of a system 9 10  11 12 #### Attribute syntax 13 14  15 16 Visibility: who is permitted to access the attribute 17 * `+` public, everybody 18 * `-` private, only the object itself 19 * `#` protected, class itself and subclasses 20 * `~` package, classes that are in the same package 21 22 `/` means that attribute value is derived from other attributes 23 24 Type: 25 * primitive data type 26 * pre-defined: Boolean, Integer, UnlimitedNatural, String 27 * User-defined: «primitive» 28 * composite: «datatype» 29 * enumerations: «enumeration» 30 31  32 33 Multiplicity: number of values an attribute may contain (as [min..max], max can be `*` meaning no limit) 34 35 `= Default`: the default value that's used if the user doesn't explicitly set a value 36 37 properties: 38 * `[readOnly]` - value can't be changed 39 * `[unique]` - no duplicates allowed 40 * `[non-unique]` - duplicates allowed 41 * `[ordered]` - fixed order of values 42 * `[unordered]` - no fixed order of values 43 44 #### Operation syntax 45 46  47 48 Similar to attributes. 49 50 parameter: 51 * direction 52 * `in`: input parameter (value is expected) 53 * `out`: output parameter (adopts a new value after execution of operation) 54 * `inout`: combined input/output 55 56  57 58 type: type of return value 59 60 #### Class variable and class operation 61 Class variable (static): defined only once per class, shared by all instances 62 63 Class operation (static): can be used without creating an instance 64 65 To distinguish class variables/operations, underline them. 66 67 ### Relationships 68 69 #### Binary association 70 Connects instances of two classes with one another. 71 72  73 74 Properties: 75 * Navigability: an object knows its partner objects, can access their visible attributes and operations (open arrow head, if not then cross). If undefined, bidirectional is assumed. 76 * Multiplicity: number of objects that can be associated with exactly one object of the opposite side (e.g. one-to-one, one-to-many...) 77 * Role: how an object is involved in an association relationship 78 * `xor` constraint: cannot be associated with both at the same time 79 80 in Java: 81 82 ```java 83 class Professor {...} 84 85 class Student { 86 public Professor[] lecturer; 87 } 88 ``` 89 90 #### n-ary association 91 More than two objects involved in the relationship, no navigation directions. 92 93  94 95 #### Association class 96 Assign attributes to relationship between classes instead of to a class. 97 98  99 100 Needed for n:m associations. 101 102 Association class vs regular class: 103 104  105 106 Can be unique or non-unique. 107 108 #### Aggregation 109 Shows that class is part of another class. 110 111 Properties: 112 * transitive: if B is part of A and C is part of B, C is also part of A 113 * asymmetric: not possible for A to be part of B and B to be part of A at the same time 114 115 ##### Shared aggregation 116 expresses weak belonging of the parts to a whole (parts also exist independently of the whole). one element can be part of multiple other elements at the same time. 117 118 Example: 119 120  121 122 ##### Composition 123 existence dependency between composite object and its parts. one part can be contained in max one composite object at a point in time. if the composite object is deleted, so are its parts. 124 125 A `Tire` can exist without a `Car`. A `Tire` belongs to max one `Car`: 126 127  128 129 #### Generalization 130 stuff from a superclass is passed to its subclass (attributes, operations, associations, aggregations) 131 132 every instance of a subclass is simultaneously an indirect instance of the superclass. subclass inherits all characteristics except private ones. generalizations are transitive. a class may have multiple superclasses/subclasses. 133 134  135 136 abstract class ensures that there are no direct instances of the superclass. 137 138  139 140 ### Creating a class diagram 141 nouns often indicate classes. adjectives indicate attribute values. verbs indicate operations. 142 143 in general, tend towards having deep classes. push complexity as low as possible in the class diagram hierarchy. 144 145 focus on: 146 * responsibility of each class (private is default, `getter` and `setter` methods) 147 * knowledge needed by each class (tend toward generality, don't focus on order of tasks) 148 * usability of operations of each class (exposed APIs should be as easy and intuitive as possible 149 150 generalization: "there is difference between research and administrative employees. some research associates hold courses, so they are lecturers." 151 152  153 154 composition: "a university consists of multiple faculties which are composed of various institutes." 155 156  157 158 binary association: "each faculty is led by a dean, who is an employee of the university" 159 160  161 162 shared aggregation: "research associates are assigned to at least one institute" 163 164  165 166 association class: "research associates can be involved in projects for a certain number of hours" 167 168  169 170 generalization: "some research associates hold courses. then they are called lecturers." 171 172  173