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46-415: The ISO 19125 standard comes in two parts. Part 1, ISO 19125-1 (SFA-CA for "common architecture"), defines a model for two-dimensional simple features, with linear interpolation between vertices, defined in a hierarchy of classes ; this part also defines representation of geometry in text and binary forms. Part 2 of the standard, ISO 19125-2 (SFA-SQL), defines a "SQL/MM" language binding API for SQL under

92-638: A someGeometryObject.isEmpty() as in Part 1, SQL/MM uses a ST_IsEmpty(...) function in SQL. The spatial extension adds the datatypes "Circularstring", "CompoundCurve", "CurvePolygon", "PolyhedralSurface", the last of which is also included into the OGC standard. It also defines the SQL/MM versions of these types and operations on them. Direct implementations of Part 2 (SQL/MM) include: Adaptations include: GeoSPARQL

138-467: A constructor and a destructor . An object expresses data type as an interface – the type of each member variable and the signature of each member function (method). A class defines an implementation of an interface, and instantiating the class results in an object that exposes the implementation via the interface. In the terms of type theory, a class is an implementation‍—‌a concrete data structure and collection of subroutines‍—‌while

184-417: A virtual machine which typically includes storage, a virtual CPU . A computer graphics polygonal model can be instantiated in order to be drawn several times in different locations in a scene which can improve the performance of rendering since a portion of the work needed to display each instance is reused. In a POSIX-oriented operating system , program instance refers to an executing process . It

230-603: A UITableView is a UIScrollView is a UIView is a UIResponder is an NSObject. In object-oriented analysis and in Unified Modelling Language (UML), an association between two classes represents a collaboration between the classes or their corresponding instances. Associations have direction; for example, a bi-directional association between two classes indicates that both of the classes are aware of their relationship. Associations may be labeled according to their name or purpose. An association role

276-487: A bounding box or proximity search". Class (computer programming) In object-oriented programming , a class defines the shared aspects of objects created from the class. The capabilities of a class differ between programming languages , but generally the shared aspects consist of state ( variables ) and behavior ( methods ) that are each either associated with a particular object or with all objects of that class. Object state can differ between each instance of

322-445: A button, and all the buttons together compose the interface (other television sets that are the same model as yours would have the same interface). In its most common form, an interface is a specification of a group of related methods without any associated implementation of the methods. A television set also has a myriad of attributes , such as size and whether it supports color, which together comprise its structure. A class represents

368-405: A class from its interface: the internal structure is made private, while public accessor methods can be used to inspect or alter such private data. Access specifiers do not necessarily control visibility , in that even private members may be visible to client external code. In some languages, an inaccessible but visible member may be referred to at runtime (for example, by a pointer returned from

414-422: A collection of objects, such as instances of Body , Engine , Tires , etc. Object modeling languages such as UML include capabilities to model various aspects of "part of" and other kinds of relations – data such as the cardinality of the objects, constraints on input and output values, etc. This information can be utilized by developer tools to generate additional code besides the basic data definitions for

460-501: A concrete sub class. An abstract class is either labeled as such explicitly or it may simply specify abstract methods (or virtual methods ). An abstract class may provide implementations of some methods, and may also specify virtual methods via signatures that are to be implemented by direct or indirect descendants of the abstract class. Before a class derived from an abstract class can be instantiated, all abstract methods of its parent classes must be implemented by some class in

506-504: A member function), but an attempt to use it by referring to the name of the member from the client code will be prevented by the type checker. The various object-oriented programming languages enforce member accessibility and visibility to various degrees, and depending on the language's type system and compilation policies, enforced at either compile time or runtime . For example, the Java language does not allow client code that accesses

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552-421: A superclass of Rectangle and Ellipse , while Square would be a subclass of Rectangle . These are all subset relations in set theory as well, i.e., all squares are rectangles but not all rectangles are squares. A common conceptual error is to mistake a part of relation with a subclass. For example, a car and truck are both kinds of vehicles and it would be appropriate to model them as subclasses of

598-601: A type is an interface . Different (concrete) classes can produce objects of the same (abstract) type (depending on type system). For example, the type (interface) Stack might be implemented by SmallStack that is fast for small stacks but scales poorly and ScalableStack that scales well but has high overhead for small stacks. A class contains data field descriptions (or properties , fields , data members , or attributes ). These are usually field types and names that will be associated with state variables at program run time; these state variables either belong to

644-491: A vehicle class. However, it would be an error to model the parts of the car as subclass relations. For example, a car is composed of an engine and body, but it would not be appropriate to model an engine or body as a subclass of a car. In object-oriented modeling these kinds of relations are typically modeled as object properties. In this example, the Car class would have a property called parts . parts would be typed to hold

690-420: Is a sub-class , and the class it is based on is its superclass . As an instance of a class, an object is constructed from a class via instantiation . Memory is allocated and initialized for the object state and a reference to the object is provided to consuming code. The object is usable until it is destroyed – its state memory is de-allocated. Most languages allow for custom logic at lifecycle events via

736-407: Is a common set of access specifiers : Although many object-oriented languages support the above access specifiers,their semantics may differ. Object-oriented design uses the access specifiers in conjunction with careful design of public method implementations to enforce class invariants—constraints on the state of the objects. A common usage of access specifiers is to separate the internal data of

782-417: Is also commonly known as a has-a relationship. For example, a class "Car" could be composed of and contain a class "Engine". Therefore, a Car has an Engine. One aspect of composition is containment, which is the enclosure of component instances by the instance that has them. If an enclosing object contains component instances by value, the components and their enclosing object have a similar lifetime . If

828-399: Is an OGC standard that is intended to allow geospatially- linked data representation and querying based on RDF and SPARQL by defining an ontology for geospatial reasoning supporting a small Simple Features (as well as DE-9IM and RCC8 ) RDFS / OWL vocabulary for GML and WKT literals. As of 2012, various NoSQL databases had very limited support for "anything more complex than

874-401: Is based on a type definition. When created, an occurrence is said to have been instantiated , and both the creation process and the result of creation are called instantiation . A class instance is an object-oriented programming (OOP) object created from a class . Each instance of a class shares a data layout but has its own memory allocation. A computer instance is an occurrence of

920-545: Is called a pure abstract base class (or pure ABC ) in C++ and is also known as an interface by users of the language. Other languages, notably Java and C#, support a variant of abstract classes called an interface via a keyword in the language. In these languages, multiple inheritance is not allowed, but a class can implement multiple interfaces. Such a class can only contain abstract publicly accessible methods. In some languages, classes can be declared in scopes other than

966-405: Is given end of an association and describes the role of the corresponding class. For example, a "subscriber" role describes the way instances of the class "Person" participate in a "subscribes-to" association with the class "Magazine". Also, a "Magazine" has the "subscribed magazine" role in the same association. Association role multiplicity describes how many instances correspond to each instance of

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1012-411: Is not an intrinsic aspect of classes. An object-based language (i.e. Classic Visual Basic ) supports classes yet does not support inheritance. A programming language may support various class relationship features. Classes can be composed of other classes, thereby establishing a compositional relationship between the enclosing class and its embedded classes. Compositional relationship between classes

1058-601: The Internet requires this level of flexibility and the technology standards such as the Web Ontology Language (OWL) are designed to support it. A similar issue is whether or not the class hierarchy can be modified at run time. Languages such as Flavors, CLOS, and Smalltalk all support this feature as part of their meta-object protocols . Since classes are themselves first-class objects, it is possible to have them dynamically alter their structure by sending them

1104-507: The appropriate messages. Other languages that focus more on strong typing such as Java and C++ do not allow the class hierarchy to be modified at run time. Semantic web objects have the capability for run time changes to classes. The rationale is similar to the justification for allowing multiple superclasses, that the Internet is so dynamic and flexible that dynamic changes to the hierarchy are required to manage this volatility. Although many class-based languages support inheritance, inheritance

1150-410: The class from outside the enclosing class. A related concept is inner types , also known as inner data type or nested type , which is a generalization of the concept of inner classes. C++ is an example of a language that supports both inner classes and inner types (via typedef declarations). A local class is a class defined within a procedure or function. Such structure limits references to

1196-431: The class name to within the scope where the class is declared. Depending on the semantic rules of the language, there may be additional restrictions on local classes compared to non-local ones. One common restriction is to disallow local class methods to access local variables of the enclosing function. For example, in C++, a local class may refer to static variables declared within its enclosing function, but may not access

1242-465: The class or specific instances of the class. In most languages, the structure defined by the class determines the layout of the memory used by its instances. Other implementations are possible: for example, objects in Python use associative key-value containers. Some programming languages such as Eiffel support specification of invariants as part of the definition of the class, and enforce them through

1288-426: The class whereas the class state is shared by all of them. The object methods include access to the object state (via an implicit or explicit parameter that references the object) whereas class methods do not. If the language supports inheritance , a class can be defined based on another class with all of its state and behavior plus additional state and behavior that further specializes the class. The specialized class

1334-597: The classes that they are derived from. For example, if "class A" inherits from "class B" and if "class B" implements the interface "interface B" then "class A" also inherits the functionality(constants and methods declaration) provided by "interface B". In languages that support access specifiers , the interface of a class is considered to be the set of public members of the class, including both methods and attributes (via implicit getter and setter methods ); any private members or internal data structures are not intended to be depended on by external code and thus are not part of

1380-502: The components are contained by reference, they may not have a similar lifetime. For example, in Objective-C 2.0: This Car class has an instance of NSString (a string object), Engine , and NSArray (an array object). Classes can be derived from one or more existing classes, thereby establishing a hierarchical relationship between the derived-from classes ( base classes , parent classes or superclasses ) and

1426-474: The derivation chain. Most object-oriented programming languages allow the programmer to specify which classes are considered abstract and will not allow these to be instantiated. For example, in Java , C# and PHP , the keyword abstract is used. In C++ , an abstract class is a class having at least one abstract method given by the appropriate syntax in that language (a pure virtual function in C++ parlance). A class consisting of only pure virtual methods

Simple Features - Misplaced Pages Continue

1472-624: The derived class ( child class or subclass ) . The relationship of the derived class to the derived-from classes is commonly known as an is-a relationship. For example, a class 'Button' could be derived from a class 'Control'. Therefore, a Button is a Control. Structural and behavioral members of the parent classes are inherited by the child class. Derived classes can define additional structural members (data fields) and behavioral members (methods) in addition to those that they inherit and are therefore specializations of their superclasses. Also, derived classes can override inherited methods if

1518-431: The full description of a television, including its attributes (structure) and buttons (interface). Getting the total number of televisions manufactured could be a static method of the television class. This method is associated with the class, yet is outside the domain of each instance of the class. A static method that finds a particular instance out of the set of all television objects is another example. The following

1564-413: The function's automatic variables . A metaclass is a class where instances are classes. A metaclass describes a common structure of a collection of classes and can implement a design pattern or describe particular kinds of classes. Metaclasses are often used to describe frameworks . Instance (computer science) In computer science, an instance is an occurrence of a software element that

1610-413: The geometries, in the object-oriented style. In general, a 2D geometry is simple if it contains no self-intersection. The specification defines DE-9IM spatial predicates and several spatial operators that can be used to generate new geometries from existing geometries. Part 2 is a SQL binding to Part 1, providing a translation of the interface to non-object-oriented environments. For example, instead of

1656-446: The global scope. There are various types of such classes. An inner class is a class defined within another class. The relationship between an inner class and its containing class can also be treated as another type of class association. An inner class is typically neither associated with instances of the enclosing class nor instantiated along with its enclosing class. Depending on the language, it may or may not be possible to refer to

1702-432: The interface. Object-oriented programming methodology dictates that the operations of any interface of a class are to be independent of each other. It results in a layered design where clients of an interface use the methods declared in the interface. An interface places no requirements for clients to invoke the operations of one interface in any particular order. This approach has the benefit that client code can assume that

1748-623: The language allows. Not all languages support multiple inheritance. For example, Java allows a class to implement multiple interfaces, but only inherit from one class. If multiple inheritance is allowed, the hierarchy is a directed acyclic graph (or DAG for short), otherwise it is a tree . The hierarchy has classes as nodes and inheritance relationships as links. Classes in the same level are more likely to be associated than classes in different levels. The levels of this hierarchy are called layers or levels of abstraction. Example (Simplified Objective-C 2.0 code, from iPhone SDK): In this example,

1794-667: The object-oriented community consider antithetical to the goals of using object classes in the first place. Understanding which class will be responsible for handling a message can get complex when dealing with more than one superclass. If used carelessly this feature can introduce some of the same system complexity and ambiguity classes were designed to avoid. Most modern object-oriented languages such as Smalltalk and Java require single inheritance at run time. For these languages, multiple inheritance may be useful for modeling but not for an implementation. However, semantic web application objects do have multiple superclasses. The volatility of

1840-473: The objects, such as error checking on get and set methods . One important question when modeling and implementing a system of object classes is whether a class can have one or more superclasses. In the real world with actual sets, it would be rare to find sets that did not intersect with more than one other set. However, while some systems such as Flavors and CLOS provide a capability for more than one parent to do so at run time introduces complexity that many in

1886-405: The operations of an interface are available for use whenever the client has access to the object. The buttons on the front of your television set are the interface between you and the electrical wiring on the other side of its plastic casing. You press the "power" button to toggle the television on and off. In this example, your particular television is the instance, each method is represented by

Simple Features - Misplaced Pages Continue

1932-507: The other class of the association. Common multiplicities are "0..1", "1..1", "1..*" and "0..*", where the "*" specifies any number of instances. There are many categories of classes, some of which overlap. In a language that supports inheritance, an abstract class , or abstract base class ( ABC ), is a class that cannot be directly instantiated. By contrast, a concrete class is a class that can be directly instantiated. Instantiation of an abstract class can occur only indirectly, via

1978-766: The prefix "ST_". The open access OGC standards cover additionally APIs for CORBA and OLE / COM , although these have lagged behind the SQL one and are not standardized by ISO. There are also adaptations to other languages covered below. The ISO/IEC 13249-3 SQL/MM Spatial extends the Simple Features data model, originally based on straight-line segments , adding circular interpolations (e.g. circular arcs ) and other features like coordinate transformations and methods for validating geometries, as well as Geography Markup Language support. The geometries are associated with spatial reference systems . The standard also specifies attributes , methods and assertions with

2024-461: The private data of a class to compile. In the C++ language, private methods are visible, but not accessible in the interface; however, they may be made invisible by explicitly declaring fully abstract classes that represent the interfaces of the class. Some languages feature other accessibility schemes: Conceptually, a superclass is a superset of its subclasses. For example, GraphicObject could be

2070-766: The programmer to define and call these special methods. Every class implements (or realizes ) an interface by providing structure and behavior. Structure consists of data and state, and behavior consists of code that specifies how methods are implemented. There is a distinction between the definition of an interface and the implementation of that interface; however, this line is blurred in many programming languages because class declarations both define and implement an interface. Some languages, however, provide features that separate interface and implementation. For example, an abstract class can define an interface without providing an implementation. Languages that support class inheritance also allow classes to inherit interfaces from

2116-653: The type system. Encapsulation of state is necessary for being able to enforce the invariants of the class. The behavior of a class or its instances is defined using methods . Methods are subroutines with the ability to operate on objects or classes. These operations may alter the state of an object or simply provide ways of accessing it. Many kinds of methods exist, but support for them varies across languages. Some types of methods are created and called by programmer code, while other special methods—such as constructors, destructors, and conversion operators—are created and called by compiler-generated code. A language may also allow

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