# dependence vs dependency [computers]

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#### agnerf

##### New Member
What's the difference between "dependence" and "dependency"? I have looked in various dictionaries, and it seems that both are defined as the state of being dependent. Dependency can also mean something that depends on something else.

I am writing computer manuals <<Link deleted>> and the situations where I want to use one of these two words can be described as follows:

A computer is doing a series of calculations: A -> B -> C -> D -> etc.
The computer is capable of doing multiple things at the same time. If each calculation depends on the previous one, i.e. if the calculation of B needs the result of A as an input, then the computer has to wait for A to finish before it can start calculating B, and B must be finished before it can start doing C, etc. The calculation takes longer time than if A, B, C, D were independent. This is called a "dependency chain". A Google search shows that "dependency chain" is more common than "dependence chain", but I can't see why?

The next situation is where A and B are independent, but the computer doesn't know this. The computer waits for A to finish before it starts calculating B because it doesn't know that B is independent of A. This is an undesired waste of time. Is this called a "false dependence" or a "false dependency"?

If dependency can mean something that depends on something else, then we can say that B is a dependency of A, but this doens't apply here because it is the link between A and B (the arrow in A -> B) that is the object of my sentence, not B. Does B have a dependence on A or a dependency on A?

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• #### panjandrum

##### Lapsed Moderator
Hello agnerf, and welcome to WordReference

Personal response to the question ...
In many contexts I believe either may be used - it depends which sounds best.
Your examples are helpful, though, because you use the term attributively. A dependency chain sounds better (to me) than a dependence chain.

False dependence or false dependency sound equally good.

#### agnerf

##### New Member
Since I am not a native English speaker, I cannot really rely on what sounds best. Does this distinction make sense:
In the calculation sequence A -> B, "dependence" is a property of B, making it dependent on A. "Dependency" is the arrow that ties A and B together and restricts or delays the calculation of B.

"Dependency" is often used to describe drug addiction. If we make the same distinction here, then "dependence" would be the state of the addict, with his mind saying: I need my fix. "Dependency" would be the imaginary string that ties the addict to his drug and restricts his freedom like a dog on a leash.

I cannot find any dictionary that gives credence to this distinction, but it would explain the current usage. What do you think?

#### panjandrum

##### Lapsed Moderator
I understand you are suggesting:
... dependence - for the state of the addict, or the variable B
... dependency - for the relationship between addict and drug, or the variable B and the variable A.

Looking around, Fowler's Modern English Usage distinguishes between dependence (the state of being dependent) and dependency (a country or province controlled by another).
That is not a great deal of help with dependency, but it supports your suggested use of dependence.

The OED has various definitions.
dependence:
2. The relation of having existence hanging upon, or conditioned by, the existence of something else; the fact of depending upon something else.
3. The relation of anything subordinate to that from which it holds, or derives support, etc.; the condition of a dependant; subjection, subordination. (Opp. to independence.)

dependency:
2. The relation of a thing (or person) to that by which it is supported; state of subjection or subordination;

I don't find any strong sense of distinction there. The entry quoted for dependency ends with "= preceding, (3)"

#### agnerf

##### New Member
Thank you for your help. It looks like the term "dependency" has arisen as an aberrant form of "dependence" and the usage of it has spread like a random meme without any clear intention of distinction .

By using the word in a published manual, I am actually contributing to developing the meaning of this word in whatever direction I decide. My manuals are downloaded from the web a few hundred times per day, so I do feel some degree of responsibility for influencing common usage. (I wonder how many people are actually reading it. It's a highly specialized topic. But I can only count how many people download it, not how many people read it ).

#### cuchuflete

##### Senior Member
The next situation is where A and B are independent, but the computer doesn't know this. The computer waits for A to finish before it starts calculating B because it doesn't know that B is independent of A. This is an undesired waste of time. Is this called a "false dependence" or a "false dependency"?
Welcome agnerf,
I don't think either term is common or especially useful. I would call it bad programming, or inadequate computer instruction. If the calculations are all done sequentially unless otherwise directed by code, than there is nothing inherent to the relationship of A and B. Rather, it is a question of what the programmer does or doesn't tell the computer to do.

Intuitively, your association of dependency with the relationship, rather than the state of a variable, is comfortable.

#### agnerf

##### New Member
I don't think either term is common or especially useful. I would call it bad programming, or inadequate computer instruction.
Thank you for joining the discussion. I deliberately simplified my example to make it comprehensible to non-technicians. I was not allowed to make a link to the actual text. The effect I am talking about is a low-level effect in the microprocessor. Avoiding this is normally the responsibility of the compiler, not the programmer. The terms are known among people working with microprocessor architecture and low-level programming.

Let me return to the discussion about wheter dependence and dependency are synonyms. I tried to look up dependency in all the dictionaries I could find in the science library, most of them from the 1960's and 70's. The explanations in the dictionaries were all different. The only meaning that all the dictionaries had in common was dependency = something that depends on something else. This may be the original meaning of dependency. If B depends on A then dependency refers to B, while dependence refers to a state or condition of B. Common usage may have drifted away from this original distinction. The older dictionaries did not mention the meaning of addiction. This may be a later usage that ignores the original distinction between dependence and dependency. Even worse is the legal term loss of dependency. This refers to A, not B.

Regarding my computer examples, dependency chain would make sense according to what I assume may be the original meaning. B is a dependency of A, C is a dependency of B, etc. This truly makes sense. But false dependency would be wrong. It is the condition or restriction that is laid on B that is false, not B itself. So the correct term would be false dependence.

#### quasar585

##### New Member
I think the difference between "dependence" and "dependency" is also related to subtly different meanings of "to depend on".

"To depend on" can mean "to rely on" (examples: "I depend on my mother to pick up the children from daycare each day", "I depend on my car for transportation", "He depends on coffee to get out of bed every morning", "We fired the babysitter because we could not depend on her").

"To depend on" can also mean "to need" or "to require", including in the sense of addictions, as well as "to be contingent on" and "to be at the mercy of". To refer to this set of meanings unambiguously, one can use the form "to be dependent on", which never means "to rely on" as far as I can tell. (Examples: "He is dependent on coffee", "He is dependent on (or depends on) medication for survival", "I am dependent on (or depend on) my mother's financial support", "We should diversify our business, because we are too dependent on cheap Chinese imports").

If used in the sense of reliance, I would always use "dependence" and never "dependency". For example: "My dependence on public transportation became a problem when my local train station was shut down. I then started driving to work". Note also that "independence" (in the sense of "I value my independence") is an antonym of this particular sense of "dependence".

When used in the sense of need, contingency, or addiction, I would usually prefer "dependency" (examples: drug dependency, financial dependency, emotional dependency). It certainly seems possible to use "dependence" in this sense as well, in which case the exact meaning might have to be determined from the context. Word order can also play a role; for example, "drug dependence" sounds more like an addiction to me, but "dependence on drugs" could suggest either addiction or reliance (as in: dependence on medication to get over a cold).

In addition, I think the word "dependency" has acquired a technical meaning in computer science, usually in the sense of requiring something as a prerequisite. For example, if a file A (say, an object code file) has a dependency on a file B (say, a source file), this means that when B is updated, then A is out of date and must be recomputed. More generally, one says that a value A has a dependency on a value B if, to compute A, one has to compute B first. One can either say that B depends on, is dependent on, or has a dependency on A; one can also say that B "is a dependency" of A or that A "has B as a dependency" (here meaning "prerequisite"). See for example the manual of GNU make, where you find phrases such as "the target has multiple dependencies". I have never seen the word "dependence" used in this technical sense.

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#### agnerf

##### New Member
More generally, one says that a value A has a dependency on a value B if, to compute A, one has to compute B first.
Thanks for the explanation. What is most confusing is that two different dictionaries I have looked in define dependency as "something dependent, especially a country or state subject to another."
In other words, if A depends on B then A is a dependency of B in political terminology, but B is a dependency of A in computer terminology. Is that right?

#### quasar585

##### New Member
Thanks for the explanation. What is most confusing is that two different dictionaries I have looked in define dependency as "something dependent, especially a country or state subject to another."
In other words, if A depends on B then A is a dependency of B in political terminology, but B is a dependency of A in computer terminology. Is that right?
Yes, that sounds right to me. One means "territory" and the other "prerequisite". They are related to two quite different meanings of "depend", namely to be governed by vs. to require as a prerequisite.

I think each of these uses is exclusive to its domain. For example, one would say that a drug addict has a dependency on drugs, but not that the drug is a dependency of the addict (as in computer science), or that the addict is a dependency of the drug (as in politics).

There are other related words that are used in specific domains. For example, if A depends on B for financial support, as in the case where B is a parent and A is a minor child, then B can claim A as a "dependent" (in Canada: "dependant") for income tax purposes. But I can't think of any other context where one would use the word dependent/dependant as a noun.

In the context of "Your promotion is dependent on good performance", one would call good performance a condition or a prerequisite, but never a dependence or dependency of promotion, and neither would one call the promotion a dependence or dependency of good performance.

If the words "depender" and "dependee" existed, they could be used to uniformly replace dependency, dependant, etc, in all the above noun senses. Gibraltar would be a depender of Britain, an object file would be a dependee of a source file, a child a depender of the parent, the drug a dependee of the addict, and the promotion a depender on the good performance. Alas, there are no such words, so we will have to live with the domain specific ones.

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