grammar - How to make sense of this construct - "、それは"

First, some real-world examples of "<名詞>、それは<名詞句>。" :

• イノセンス、それはいのち (catchphrase for the movie イノセンス)


• リゾートホテル、それは[極上]{ごくじょう}のサービスに[心]{こころ}[満]{み}たされる[空間]{くうかん} (catchphrase used by a certain resort hotel)


• 歓{よろこ}び。それはBMW。 (catchphrase for the Japanese market used by BMW)

Is it correct to say that these are formed by "left dislocation" and "体言止{たいげんど}め"?

For instance, the underlying sentence of the first example, I think, is

イノセンスはいのちだ

"Dislocation" is a grammatical term describing a sentence structure in which one constituent is taken out of its normal place of occurrence, either to the left side or the right side. The dislocated element's original place is often occupied by a pronoun. (Heavily drawn from Wikipedia.) For example, "These things, they take time."

Applying left dislocation turns the sentence into:

イノセンス、それはいのちだ

"体言止め" is a figure of speech in which a sentence is terminated by a noun or a noun phrase.

イノセンス、それはいのち

All seem nice and well, but I'm not sure because I couldn't find any source talking about this construct in any way. Is the hypothesis correct, or am I missing something? Are there other possibilities?

Edit:

I did find this chiebukuro Q&A which states the English equivalent of the construct is "extraposition." It lists examples like "The demands, restrictions, pressure, fatigue, ― they spoiled the fun." Inferring from this comment to a Language Log entry, this type of extraposition is now classified as left dislocation.

So...whatever the grammatical term is, there's one supporting view that a transformation is in the work here which extracts the topic and places it outside the normal sentence structure.

Answer

For the following sentence:

イノセンス、それはいのち。

This sentence divided in [文節]{ぶんせつ} will be:

• [独立語]{どくりつご}: イノセンス


• [主語]{しゅご}: それは


• [述語]{じゅつご}: いのち

So イノセンス will be a 独立語.

And to be more precise, 独立語 are divided in 4 categories:

• [感動]{かんどう} (eg: おお、びっくりした。)


• [呼]{よ}びかけ (eg: おい、行かないでください。)


• [応対]{おうたい} (eg: はい、そうです。)


• [提示]{ていじ} (eg: イノセンス、それはいのち。)

So in this case イノセンス will be a [提示独立語]{ていじどくりつご}.

提示独立語 can be easily confused with the 主語 but they are not, most of the time they will be followed by a [指示語]{しじご} like 'それは'.

独立語 are weakly tied to other 文節 and can be separated in different sentence like in your BMW example.

The main purpose of this construction is to put emphasis on the topic. That explains why it is mainly used for advertising and speechs.

I suppose it can assimilated to English constructions like:

Freedom! It is what we are fighting for.

体言止め seems a little different regarding the Wikipedia page you linked, it is about inverting the order of 主語 and 述語 and is used when there is a verb or an adjective in the sentence.

So inspired by the example sentence, 'いのちであるイノセンス。' will be a 体言止め (normal sentence being 'いのちはイノセンスです。').