What's the difference between data and code?

Question

To take an example, consider a set of discounts available to a supermarket shopper.

We could define these rules as data in some standard fashion (lists of qualifyin

Answer 1

Huge difference. Data is a given to system while code is a part of system.

Wrong data is senseless: our code===handler is good and what you put that you take, it is not a trouble of system that you meant something else. But if code is bad - system is bad.

In example, let's consider some JSON, some bad code parser.js by me and let's say good V8. For my system bad parser.js is a code and my system works wrong. But for Google system my bad parser is data that no how says about quality of V8.

The question is very practical, no sophistic. https://en.wikipedia.org/wiki/Systems_engineering tries to make good answer and money.

Answer 2

Relationship between code and data is as follows:

code after compiled to a program processes the data while execution

program can extract data, transform data, load data, generate data ...

Also program can extract code, transform code, load code, generate code tooooooo...

Hence code without compiled or interperator is useless, data is always worth..., but code after compiled can do all the above activities....

For eg)

Sourcecontrolsystem process Sourcecodes

here source code itself is a code

Backupscripts process files

here files is a data and so on...

Answer 3

The important note is that you want to separate out the part of your code that will execute the same every time, (i.e. applying a discount) from the part of your code which could change (i.e. the products to be discounted, or the % of the discount, etc.)

This is simply for safety. If a discount changes, you won't have to re-write your discount code, you'll only need to go into your discounts repository (DB, or app file, or xml file, or however you choose to implement it) and make a small change to a number.

Also, if the discount code is separated into an XML file, then you can give the entire application to a manager, and with sufficient instructions, they won't need to pester you whenever they want to change the discount rates.

When you mix in data and code, you are exponentially increasing the odds of breaking when anything changes. So, as leppie said, you need to extract the constantly changing parts, and put them in a separate place.

Answer 4

Code is any data which can be executed. Now since all data is used as input to some program at some point of time, it can be said that this data is executed by a program! Thus your program acts as a virtual machine for your data. Hence in theory there is no difference between data and code!

In the end what matters is software engineering/development considerations like performance, efficiency etc. For example data driven programs may not be as efficient as programs which have hard coded (and hence fragile) conditional statements. Hence I choose to define code as any data which can be efficiently executed and all else being plain data.

It's a tradeoff between flexibility and efficiency. Executable data (like XML rules) offers more flexibility (sometimes) while the same data/rules when coded as part of the application will run more efficiently but changing it frequently becomes cumbersome. In other words executable data is easy to deploy but is inefficient and vice-versa. So ultimately the decision rests with you - the software designer.

Please correct me if I wrong.

Answer 5

The line between data and code (program) is blurry. It's ultimately just a question of terminology - for example, you could say that data is everything that is not code. But, as you wrote, they can be happily mixed together (although usually it's better to keep them separate).

Answer 6

I would say that the distinction between data, code and configuration is something to be made within the context of a particular component. Sometimes it's obvious, sometimes less so.

For example, to a compiler, the source code it consumes and the object code it creates are both data - and should be separated from the compiler's own code.

In your case you seem to be describing the option of a particularly powerful configuration file, which can contain code. Much as, for example, the GIMP lets you 'configure' plugins using Scheme. As the developer of the component that reads this configuration, you would think of it as data. When working at a different level -- writing the configuration -- you would think of it as code.

This is a very powerful way of designing.

Applying this to the underlying question ("How would you code the above example?"), one option might be to adopt or design a high level Domain Specific Language (DSL) for specifying rules. At startup, or when first required, the server reads the rule and executes it.

Provide an admin interface allowing the administrator to

• test a new rule file
• replace the current configuration with that from a new rule file

... all of which would happen at runtime.

A DSL might be something as simple as a table parser or an XML parser, or it could be something as sophisticated as a scripting language. From C, it's easy to embed Python or Lua. From Java it's easy to embed Groovy or Clojure.

You could switch in compiled code at runtime, with clever linking or classloader tricks. This seems more difficult and less valuable than the embedded DSL option, in my opinion.