Are 'array elements' and 'array values' the same?

Question

Array := {"title": "Book Title", "author": "John Doe"}

Some people use the following terminology:

• title and author are keys.

• Book Title and John Doe are values.

• "title": "Book Title" and "author": "John Doe" are elements (= key-value pairs).

But some people - this one:

• Book Title and John Doe are elements (= values). (These words are used as a synonyms.)
• "title": "Book Title" and "author": "John Doe" are key-element pairs (= key-value pairs).

Which terminology is correct? Does it exist at all?

Answer 1

The term element mean a distinct object that is member of a set. This terminology originates from the mathematical set theory. It is used in computer science algorithms with the same meaning, for any kind of collections.

Arrays, be it classical indexed arrays, or more elaborate associative arrays are a data structure that represents the relation between a key (or index, in the case of indexed arrays) and a value.

The element is not the really value. The value alone is not sufficient: they have no identity, and two same values cannot be distinguished. Example:

string colour[] = { "red", "blue", "red" }     // language with classical arrays
Array := {"title": "Doe", "author": "Doe"}     // language with associative arrays

If the values would really be the elements, how would you understand "swaping two elements", for example the "red" and the "blue" ? What's missing here to say which "red" you want to swap ? The key (or index) !

Now, it is not possible to give an accurate definition without considering mutablility:

• If the elements are immutable, the combination key-value (or index-value) is a better candidate for being an element than the value alone. 0-red, 1-blue, 2-red are distinct elements.

• If the elements are mutable, the combination key-value no longer defines correctly the element. In this semantic, if I change colour[1] from "red" to "green", it's still the same element, but with a new value. Here, the element is the unique object associated with the key/index.

Answer 2

Array := {"title": "Book Title", "author": "John Doe"}

Most languages don't refer to that structure as an array (the only major exception I know of is PHP). It's more commonly called a dictionary or a map; those structures have keys and values. A proper array is 'just' a list of elements/values (either term is correct); an example would be ["John", "Jane", "Bob"].

You could interpret a dictionary/map as an array of key-value pairs, but that's usually the wrong way to think of it. An array imposes a certain ordering (in my previous example, "John" precedes "Jane" and "Jane" precedes "Bob") and each element has an index (the index of "John" is 0, the index of "Jane" is 1). The ordering of key-value pairs in dictionaries is usually indeterminate.

Answer 3

I’m skipping the “key-value” part because other answers talk about it. It just emphasizes that “array” gets used a lot of different ways.

Classically, an array represents a contiguous block of memory. The name of the array dereferences to the start of the block and “the name” of each element is an offset in the memory block. In other words, historically the array is a low level data structure and a thin abstraction over sequential memory addresses.

In this context, an element of the array can mean passing by reference. An array value suggests passing by value. Changing an array element changes the array. Changing an array value might mean only changing a local value without modifying the array data structure.

Again, this is only one context and what someone actually means depends on what they actually mean. But it helps to know what they might mean before discovering that an array is still holding stale values.