10

Source: The Illustrated Network—How TCP/IP Works in a Modern Network by Walter Goralski (2009)

Example:

Bridges operate at the data link layer and normally deliver frames within the same broadcast domain based on MAC address.

Asked a friend of mine who's a native English speaker from America and he said that the sentence is fine as it is, but what exactly makes you as a speaker of English say it in that particular way? Why not, for example, just say based on MAC addresses?

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    The usage "based on MAC address" here is an ellipsis of the definite article. The definite article is "understood". I don't know why, but it's idiomatic to do this in technical and scientific writing. – P. E. Dant Nov 17 '16 at 9:46
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    "an ellipsis of the definite article" -- what does that really mean? Well, that means the article is omitted! Duh! Guess what, I kind of see that there is no article! – Michael Rybkin Nov 17 '16 at 9:52
  • The fact that we're simply dealing with idiomatic usage here can more or less count as an explanation. What would be absolutely wonderful if you could just give a bunch of examples that share a similar pattern with the example in question. – Michael Rybkin Nov 17 '16 at 9:55
  • Something tells me though that we could just as easily substitute "based on MAC address" with "based on MAC address information" and the sentence would sound equally fine because the word "information" is alway uncountable and typically doesn't take an article. I think that observation in fact might help us arrive at a viable explanation to the original question. – Michael Rybkin Nov 17 '16 at 10:01
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    I would say that "based on MAC address" describes what is going to happen with each individual delivery. It's like saying "I arranged these numbers by size" (not "by sizes") – MPW Nov 17 '16 at 17:14
16

Consider:

In the US, a person cannot be discriminated against based on race, color, religion, sex, or national origin.

When referring to a factor on which a decision or action is based, we refer to the factor in the singular. We do not say "based on races, colors, religions, sexes, or national origins". That the decision or action may affect many individuals (the entire population in my example, all packets in the domain in the OP's example) is not relevant, because we are referring to the factor as factor.

discriminated against .... based on {list of factors}

deliver frames ... based on {factor}

I chose the car based on color.

I may have looked at quite a few cars having a variety of colors, but the factor or criterion on which I based my choice was color.

P.S. See this related answer. We are referring not to the property content (e.g. "blue") but to the property generically or in abstract terms as attribute. Which attribute of the car did I base my choice on? Top speed? Number of doors? Fuel-economy? Reliability rating? Color?

  • I guess the OP would be okay with the singular if the entity noun is in singular, too. What if your examples are changed to "people" and "cars"? Wouldn't the plural be possible, too? – Damkerng T. Nov 17 '16 at 12:22
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    The plural has no effect. I chose the cars based on color = the criterion I used when making my choice(s) was color. This would be idiomatic: "I chose the cars based on their colors" but this would not be idiomatic: "I chose the cars based on colors". – Tᴚoɯɐuo Nov 17 '16 at 12:24
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    +1. The same holds for (certain senses of) by: "We grouped the oranges by shape and size." – ruakh Nov 18 '16 at 0:02
  • The problem with your example is that although the words "race", "color", "religion", "sex" and "national origin" can have countable equivalents, they are really uncountable while "MAC address" is always a count noun. It's intrinsically a count noun. There is no uncountable equivalent for this word. You see what I mean? That's what really made me ponder over the sentence. – Michael Rybkin Nov 18 '16 at 6:16
  • Would it be possible for you to come up with an example that uses, let's say, the word "fork" (it might turn out to be a silly-sounding example though) or any other noun that's always countable? – Michael Rybkin Nov 18 '16 at 6:22
15

If we use the phrase based on MAC addresses, although it might have the correct meaning for the bridge as a whole, it conveys the incorrect meaning regarding the mechanism used for individual frame delivery. The pedantically correct sentence (which has been elided) would be:

Bridges operate at the data link layer and normally deliver frames within the same broadcast domain based on the MAC address contained within each frame.

This makes it clear it is a singular MAC address that is used to make the delivery. If we changed to the plural it would imply that several MAC addresses are used in the delivery of each frame, which is incorrect. Yes, many MAC addresses are used in the delivery of many frames but the choice of singular rather than plural conveys technical information.

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    This is undeniable, but it is also undeniable that ellipsis of definite article (sic) is endemic in technical writing to the extent that many documents read as if translated from Russian. – P. E. Dant Nov 17 '16 at 11:08
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    I don't argue with the grammar side of this, but a curious thing about Ethernet is that each Ethernet frame has two MAC addresses, destination and source. I suppose it's fair to say that "based on MAC address" implies "based on the destination MAC address of each frame". :-) – Damkerng T. Nov 17 '16 at 11:58
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    @DamkerngT. Happy to be out pedanted! – Brian Tompsett - 汤莱恩 Nov 17 '16 at 11:59
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    The meat of Mr Monster's question is "...what exactly makes you as a speaker of English say it in that particular way?" The ellipsis of the article here treats "MAC address" as an uncountable noun, even though, technically, it's a noun with a count of 2! This kind of thing is very common. It sounds right, and reads right, but damned if I can answer "what exactly makes" us do it this way. – P. E. Dant Nov 17 '16 at 20:43
10

How about this:

"We sort the list based on the name."
"We choose the item based on the price."
"We don't get the item if it says it's 'Red'."

In all of these, the last word describes what is special about the items in the collection. In other words, it talks about an attribute of one item in the collection - which even though that attribute is held by all the items in the collection, the specific item's attribute is looked at to make the comparison.

  • I think this answer gets the closest to trying to say "why" we do it this way. I'd add to this that this construction implies that there is exactly one instance of this attribute on each object. So in the original example, "...based on MAC address" implies that there is one "correct" MAC address for each data packet in question. – Cort Ammon Nov 18 '16 at 3:24

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