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 July 6th, 2013, 02:16 PM #1 Newbie   Joined: Jul 2013 Posts: 1 Thanks: 0 How to compare two objects? Dear all, Please help me with finding a formal definition of what an object is and how to compare two objects. To illustrate, if one is asked to compare, for example, two balls given to him or her, the comparison will be between the balls properties (size, weight, color, material they are made of, etc.). It is impossible to compare just objects without comparing their properties. We know it from day-to-day life, although I need references to formal definitions of “object” and “object comparison”. I dag tons of materials available on-line, mainly related to philosophy art, but didn’t find clear definitions neither for an object nor for objects comparison. All explanations of what an object is and how the objects are compared are quite extensive and only lead to the awareness of these concepts but to their clear definition. I am asking you for a reference to clear and short statements of what an object is and how to compare objects. Particularly, I would be more than happy if someone could provide a reference just stating something like “Objects are compared by comparing their properties”. It would be enough, but I need a reference to only a monograph with the author(s) known in the scientific world, or an encyclopedia, or a university textbook, or an article in a scientific publication or something similar, but not to a Wikipedia or the like… Thank you in advance Sincerely yours Natalia from RU
July 6th, 2013, 03:27 PM   #2
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Re: How to compare two objects?

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 Originally Posted by Natalia Dear all, Please help me with finding a formal definition of what an object is and how to compare two objects. To illustrate, if one is asked to compare, for example, two balls given to him or her, the comparison will be between the balls properties (size, weight, color, material they are made of, etc.). It is impossible to compare just objects without comparing their properties. We know it from day-to-day life, although I need references to formal definitions of “object” and “object comparison”. I dag tons of materials available on-line, mainly related to philosophy art, but didn’t find clear definitions neither for an object nor for objects comparison. All explanations of what an object is and how the objects are compared are quite extensive and only lead to the awareness of these concepts but to their clear definition. I am asking you for a reference to clear and short statements of what an object is and how to compare objects. Particularly, I would be more than happy if someone could provide a reference just stating something like “Objects are compared by comparing their properties”. It would be enough, but I need a reference to only a monograph with the author(s) known in the scientific world, or an encyclopedia, or a university textbook, or an article in a scientific publication or something similar, but not to a Wikipedia or the like…
You can't do that. You can only build an abstract model that encapsulates some of the properties you deem important; and then compare on those properties.

For example, any two peanuts are pretty much interchangeable; but no two are exactly alike.

I'm thinking of your question in terms of computer modeling. We have a thing in the real world: a person, say. We can't tell the computer to understand what a person is. Instead what we do is build a model. We define a thing called a "person" and we say that a person has certain attributes: name, height, weight, age, gender, income, bank balance. That becomes our definition of a person in, say, a marketing database.

In a medical database perhaps a person's attributes include their medical history and details of their health insurance plan.

In a video game our definition of a person includes all the things they can do: run, shoot, hide, pick up objects, walk down a maze of twisty little passages, all alike ...

In reality, a person is all of those things. But in each computer application, or problem domain if you want to call it that, a "person" is a defined term, consisting of some attributes and capabilities. In fact in object-oriented design theory, that's exactly what an object is: a bundle of attributes and capabilities.

So you can never say, given two objects in the world, whether or not they are identical. Is this peanut the same as that one? Pretty much. But they are not the same. Not the same shape, not the same location in space, not the same molecules.

Comparing objects depends on the abstractions we use to formally manipulate the objects. We can't do the comparison without starting from the abstract model.

Objects are compared by first defining an abstract model consisting of those properties that you regard as important for your particular application or problem domain; and then, by comparing the two objects with respect to those properties.

So for example if I want to compare Barack Obama to Hillary Clinton and I only care about political rank; then they are both Democratic politicians; but he is the president and she is the former first lady and former Secretary of State. But if I am only concerned about biology, then they are both human but he is male and she is female.

The abstract model must precede any comparison. Otherwise, every object in the universe is unique.

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