What is the difference between an Object in Object Oriented Programming and a Node in OPC address space?
A typtical Object has Attributes and Methods. A Node seems to have the identical properties, but is just called "Node".
The two are completely different concepts.
A Node in OPC UA is an entity that consists of a set of well-defined Attributes (you can't influence which ones are allowed and, most importantly, can't invent new ones).
An Object in OOP is a way to arrange data in code that mimics a physical entity.
So there are plenty of OOP Objects that will never be Nodes, but it's pretty straightforward to implement an OPC UA Node for an OPC UA application using an OOP Object.
(To add to the confusion, there are OPC UA Objects, too, all of which are a special type of OPC UA Nodes. Perhaps that's where the mixup happened?)
An Object in Object Oriented programming consists of Fields( in simple sense Variables) through which methods from a class of same type can be invoked.
A Node in OPC in the Information model contains Attributes that are specific to the node and references to other nodes.Methods could also be invoked on the server from a node. Each node has a NodeId that uniquely identifies a node in OPC server information model. Nodes provides a rich method of modelling real world entities(eg: Electronic valve) to be used in data exchange and communcation.
In some sense Node is an Object in the OPC server that has reference to other objects and methods that can be invoked.
Related
I am building a system with no classes and objects, only a database. And I was wondering if it is correct to implement the sequence diagram with System and Database as the only objects in the diagram as shown in the picture.
Extract of My Sequence Diagram
You can use a sequence diagram to model exchanges not only between instances of classes, but also between instances of components or subsystems. This can be extended to systems if you’re modelling a system of systems. So your approach is perfectly acceptable (and it can really help).
By the way, the fact that a DBMS is not an object in the sense of OOP, does not prevent you from modeling it as an object, since it is encapsulated, has an internal state, and offers behavior via a well-defined interface.
The only ambiguous thing in your diagram is the actor, since lifelines should be internal to the system whereas actors are external. But it’s a common practice, even if messages exchanged are not as formally defined as one would expect in a traditional sequence diagram.
I usually try to encapsulate my code, meaning each objects works on its data via public methods. The problem is, that a lot of stakeholder/other objects of an object lead to a lot of requirements and thus a lot of methods in this object, which are then only used by one stakeholder. In such a scenario, should I rather pass the raw data to the stakeholder, so that it can process the data itself?
When should an object process its own data for other objects (offering methods) and when should it simply return its data (via getters) to let the caller do the processing itself?
I think it depends on many factors such as:
purpose of class (some real world object)
data that object has (description of this object)
desired behavior (some actions of this behavior)
For example, we have two objects:
a big bucket with water
kettle.
Then we can ask myself:
can big bucket have method boil() or should big bucket just have method giveWater()? So it can be concluded that bucket of water should just expose getter for exposing water for other users such as kettle
And by using this technique you can decide whether should an object process its own data for other objects (offering methods) and when should it simply return its data (via getters)
In addition, you should apply Single Responsibility Principle of SOLID in your classes. As Robert C. Martin says:
Martin defines a responsibility as a reason to change, and concludes
that a class or module should have one, and only one, reason to be
changed (e.g. rewritten).
So SRP defines a responsibility of a class as a reason to change, and states that a class might only have one reason to change.
So if someone edits logging code in class Radio, then it means that she/he violates SRP principle. She/he should edit logging code in Log class. These classes can communicate through references or composition.
I am trying to understand how to classify the classes as boundary/control/entity classes. I can understand boundary and entity classes although my understanding may not beperfect. Boundary is the classes which interacts with the user. So the classes used for the userinterface will be boundary classes. Entity class handles data. So entities I use in the ER diagram will be entity classes. But I understand nothing why control object is used. It is said that control object is used to encapsulate domain functionalities. What if the control classes are not used. Can you please explain me with example.I found some explaination but I am still confused.Why boundary should not interact directly with entity? There are also classes which are not boundary/control/entity. What are they?
Background
The Entity/Boundary/Control approach was introduced by Ivar Jacobson in 1992 as part of his use case driven Objectory development method.
At that time Jacobson used the terminology Entity/Interface/Control. The strange circle notation that you can find in relaction with ECB was already used in his books in 1992 and in 1994. By the way, the use case of his methods were integrated into UML and his development process was merged into RUP, when Rational acquired Objectory.
The idea behind his method was to adopt a very logic and formal and deductive analysis and design approach. It starts with identifying the systems behavioral requirement with use cases. Each link of use case to the outside world would then be represented as an interface object responsible for encapsulating completely the user interface.
Each use case would be represented as one or several control objects:
Control object: An object that encapsulates functionality of one or
several use cases - I.Jacobson in The Object Advantage, ACM Press, 1994
Finally the business objects managed by the system can be partly inferred from the use cases, and during the analysis.
Additional information
The fundaments of the Iconix process were introduced in 1999 as part of the book "Use Case Driven Object Modeling with UML" by Rosenberg & Stephen. Some additional robustness constraints were introduced, certainly to improve separation of concerns. For example, the direct link between entity and boundary is prohibited. Everything has to be channelled through control objects:
Control objects (which we usually call controllers because they often
aren't real objects), serve as the "glue" between boundary objects and
entity objects - D.Rosenberg, in the linked DDJ article.
They add a recommendation to clarify the intent :
Both boundary objects and entity objects are nouns, and controllers
are verbs.
Conclusion
So the principle is that the control object represents the business logic offered by use cases, interacting on one side with the boundaries, and on the other side with the entities. Control objects can't be invoked/accessed directly by the outside world.
If you would want to avoid the control objects, you would have a boundary objects with methods corresponding to the verbs/functions/use-cases that your system is supposed to provide. This wouldn't be according to the modern ECB, but perfectly valid according to Jacobson's original approach. Nevertheless your boundary would no longer comply with the single responsibility principle of a SOLID design.
Boundary interact with actors (e.g. users).
Entity classes represent data.
Control mediates between the boundary and the entities (e.g. executes an operation on the entities)
Source: http://www.cs.sjsu.edu/~pearce/modules/patterns/enterprise/ecb/ecb.htm
The control classes contain the business logic. It's the most important part of a system. While the boundary just controls whether the text is green or blue (very basically) and the entities control whether data is stored in text files or databases (also very basically) the control classes do all the business logic. What to change in the entity when the boundary send mouse/keyboard events an vice verse what to show from the entities in the boundary.
I have to model an already written object library in UML.Now, I've read tutorials and examples, but they only discuss real life examples such as cars and their components or students, professors and classes. Obviously, those are very easy to model in UML. However, the particular thing about this library is that it contains both classes which define different objects and Windows forms that allow the user to interact with them. A form can both represent an object graphically by all kinds of Windows controls and allow the user to modify it. In addition, there's also a sort of 'main class' which uploads and downloads these objects to and from a remote server. Obviously, this 'main class' handles all aspects of communication and acts like a data channel. So, schematically this is how the library looks like:
Object1Class [Field1, Field2, ....]
Object2Class [Field1, Field2, ....]
...
Object1Form
Object2Form
...
MainClass (NB: this class doesn't create any forms. It just uses the objects created by the forms. The forms are used externally by software systems which rely on this library)
So how would I model this using UML?
Thanks in advcance,
AlgolDocks
I did not understand the context but it seems to me that a good reverse of the object library could be a good start. You can get class and sequence diagram showing static architecture or methods interactions. You can also revers more than one library which is really useful if you need to understand what is going on.
Having said that I found an example of Jar reverse engineering at: http://www.ejb3.org/jar_file_reverse/jar_file_reverse.html
You should certainly have other tools providing this kind of reverse but I don't know about them providing such an advanced feature therefore can not help further.
I'm using C++ (with the Qt library) to make a simple domain modeled application. I am writing my own O/R mapping classes. As this application will grow in the future I'm trying to keep a clean codebase with clearly separated layers.
The problem I am having is when and where to load aggregate roots that are referenced in an object in another module. (I am using Eric Evans' use of the word "module" here, from the DDD book.)
I currently have a simple object called Client that sits in the ClientModule module. In the PermitModule I have a Permit object. (the reality is more complex but for brevity I'll stick to those two objects, since they are the aggregate roots) The Permit object has a reference to a Client as applicant. This is my domain model.
From the bottom up, I have an Infrastructure Layer that contains O/R mapping classes and concrete implementations of Repository objects. So I would have a ClientMapper, ClientRepositoryDb, PermitMapper, and PermitRepositoryDb classes here.
Next is the Domain Layer that contains the domain model (Client and Permit classes) plus the repository interfaces ClientRepository and PermitRepository.
Above that I have an Application Layer and then a Presentation Layer but those don't matter in this example.
My question is should the relationship between Permit and Client be loaded in the PermitMapper class or in the PermitRepository class. Or is there some other way of doing it?
This goes not only for loading objects but also for saving them and removing them.
I've gone with the approach that my Mapper classes load themselves fully.
I'm not a Java developer but I wonder how Hibernate (et al) does it?