Could there be a base class for customers, employees and suppliers?
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In a software for a company, we usually have customers, employees and suppliers in what regards humans. Therefore a reasonable (meaning a good one) OOP approach would be to have a class 'Persons' with attributes such as name, surname, address etc. and then let the classes 'Customers', 'Employees' and 'Suppliers' derive from the class 'Persons'. But, on a second thought there is a problem. How do we deal with customers and suppliers which are companies?
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Add a class called Company and then add an optional CompanyId (can be null) field to the Person class. That way you can deal with individuals and or individuals from a company.
"You get that on the big jobs."
I'd argue the other way around. Company is not an attribute of a person, but a person - as in a contact - is an attribute of a company.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Richard MacCutchan wrote:
Sorry but you are asking for a tutorial on OOP
Well, not really. I 've read already many books about OOP, even studied and done some programmes. I found out that there can be solutions and concepts which vary a lot. In the above example there could be two solutions with or without inheritance between the classes I mentioned. And both could be acceptable and good. Both? Maybe? THat's why I asked here, to get answers from more experienced members. This cannot be done in a tutorial. Thanks for the links.
If you want a good insight into design, try The Gang of Four[^], it provides some very good non-language specific information. If you are serious about design, I would suggest it as a must-have.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Nagy Vilmos wrote:
From experience, there should be a
Personthat is used to represent a physical being [and maybe a role in some cases] and anOrganisationto represent companies [which will havePersoncontacts.Do you mean in a form of nested classes?
No. I mean as candidate classes. Begin by writing out in plain English [other languages are available] what you want to do. As an example, your system could be described thus:
Requirements:
Provide software to manage the relationships between the company and it's suppliers and customers. All the contacts can be either individual people or companies. Any company will have one or more contact. Orders are recieved from customers and placed with suppliers for the provision of Widgets and associated products. Every order received will result in an invoice being raised by the accounting system. Orders placed with suppliers will be filled and invoices for payment will be sent to the accounting system. Each order [inbound or outbound] will have a billing address and a delivery address, these need not be the same. Each customer can have default addresses associated with it.
From this initial requirement, you can take out all the nouns and noun phrases. These are your candidate classes. The next stage is to decide which ones are classes in their own right and which are attributes. Often a lot of candidates can be reduced. As an exercise, I would recommend giving this a go and see where it takes you.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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I'd argue the other way around. Company is not an attribute of a person, but a person - as in a contact - is an attribute of a company.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
Agreed: start with the largest discreet object and work back from that.
"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." Red Adair. nils illegitimus carborundum me, me, me
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I understand what you are saying but there is no real project. What I am really trying to do, is to find out why and where to use a base class in a hypothetical (but indeed very common) design problematic of, let's say, an ERP software. If we narrow the problem to customers and employees, and assuming that customers are only individuals, it is obvious that both are persons, therefore a base class Persons and two inherited classes of Customers and Employees seems to be very reasonable. But do we need to build a base class in our programme and if yes why? What is the real practical purpose of doing so? In my opinion this generalization of our two "real" classes seems to complicate designing without any having any profit from it. That is my real question to the forum (although some of the answers above have already answered that too).
nstk wrote:
What I am really trying to do, is to find out why and where to use a base class in a hypothetical (but indeed very common) design problematic of, let's say, an ERP software.
Again...you start with the problem domain and it defines the classes. If you don't have a problem domain then you cannot defined classes.
nstk wrote:
But do we need to build a base class in our programme and if yes why?
Because the problem domain has requirements that specify that sort of implementation. Or because the problem domain lead to a specific implmentation and that implementation is best implemented that way.
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No. I mean as candidate classes. Begin by writing out in plain English [other languages are available] what you want to do. As an example, your system could be described thus:
Requirements:
Provide software to manage the relationships between the company and it's suppliers and customers. All the contacts can be either individual people or companies. Any company will have one or more contact. Orders are recieved from customers and placed with suppliers for the provision of Widgets and associated products. Every order received will result in an invoice being raised by the accounting system. Orders placed with suppliers will be filled and invoices for payment will be sent to the accounting system. Each order [inbound or outbound] will have a billing address and a delivery address, these need not be the same. Each customer can have default addresses associated with it.
From this initial requirement, you can take out all the nouns and noun phrases. These are your candidate classes. The next stage is to decide which ones are classes in their own right and which are attributes. Often a lot of candidates can be reduced. As an exercise, I would recommend giving this a go and see where it takes you.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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I'd argue the other way around. Company is not an attribute of a person, but a person - as in a contact - is an attribute of a company.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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In a software for a company, we usually have customers, employees and suppliers in what regards humans. Therefore a reasonable (meaning a good one) OOP approach would be to have a class 'Persons' with attributes such as name, surname, address etc. and then let the classes 'Customers', 'Employees' and 'Suppliers' derive from the class 'Persons'. But, on a second thought there is a problem. How do we deal with customers and suppliers which are companies?
I would suggest looking at good MDM[^] designs as they obviously deal with it. I am not saying make yourself an MDM system (or buy/donwload one). I am just saying that MDM deals with so many 'entities' and they of course try to abstract out the overlapping info. I have never really looked into it too much but have dealt with MDM groups. Sometimes their 'naming' is off so it can be confusing, but in the end they get the job done. So if you find some info on MDM architecture you might stumble on to a good base class design.
Computers have been intelligent for a long time now. It just so happens that the program writers are about as effective as a room full of monkeys trying to crank out a copy of Hamlet.
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And all the customers who are buying products and services for their own personal use. They don't have companies so what do you do about them?
"You get that on the big jobs."
You missed the BIG POINT earlier. A customer is a person or a company, A company also has a person as a contact. I almost feel an article...
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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You missed the BIG POINT earlier. A customer is a person or a company, A company also has a person as a contact. I almost feel an article...
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Nagy Vilmos wrote:
A customer is a person or a company, A company also has a person as a contact.
What about putting the Persons class as a nested class in the Company class in that case? Complicated?
Not a good idea. The attributes of a person - name, date of birth, sex, etc - are independent of the role they perform. A decent representation of a person will be reusable if you ignore how it is used. Similarly, the concept of a company is independent of the problem domain. A company has employees but, and this is true in real life as much as in a program, the employee does not have a company.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Thanks for your effort, I really appreciate this great help. I will indeed develop this as an exercise and if there is something to discuss I will write it here. :)
Here is a simple set of candidate classes:
+------------+ | Customer | | | +------------+ | v+------------+ +------------+ +------------+
| Supplier |--->| Contact |--->| Person |
| | | | | |
+------------+ +------------+ +------------+
|
+------+--------+
| impliments |
+------------+ +------------+
| Company | | Individual |
| | | |
+------------+ +------------+
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Here is a simple set of candidate classes:
+------------+ | Customer | | | +------------+ | v+------------+ +------------+ +------------+
| Supplier |--->| Contact |--->| Person |
| | | | | |
+------------+ +------------+ +------------+
|
+------+--------+
| impliments |
+------------+ +------------+
| Company | | Individual |
| | | |
+------------+ +------------+
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Shouldn't Person inherit from Contact? The arrow direction between them indicates the opposite situation.
The arrows represents a reference, so a Contact 'has a' Person.
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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You missed the BIG POINT earlier. A customer is a person or a company, A company also has a person as a contact. I almost feel an article...
Panic, Chaos, Destruction. My work here is done. Drink. Get drunk. Fall over - P O'H OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
I still missed the big point but if you do get around to writing the article, It would be interesting. I guess your talking about some kind of interface that both person and customer implement. Anyway I've just spent the last month discovering values such as the "delivery contact name" being stored in the weather_sunny field. :mad: So I'm a bit paranoid about such things at the moment.
"You get that on the big jobs."