As far as I understand some basic principles of the Semantic Web (especially the Resource Description Framework RDF), the semantic is described in tripels with subject, predicate and object.
So for example I can express
Pancake consistsOf Egg
Pancake consistsOf Flour
Pancake consistsOf Milk
Pancake producibleBy PancakeRecipe1
Pancake producibleBy PancakeRecipe2
Main question: How to describe process steps and time dependent statements with Semantic Web triples?
Process steps, amounts
How can I express amounts in a process step with tripels? For example the instruction "use 2 eggs". Maybe this is an approach: PancakeRecipe1 useEggs 2. But this would imply that when I want to offer a universal process description (not only for pancakes), I have to add a predicate for every thing that could ever be part of everything else (even those things that are unknown at the moment).
Another approach: PancakeRecipe1 use2 Egg. This would imply that I have to add a predicate for every amount (even floats). Not practical.
A third approach:
PancakeRecipe1 use 2Eggs
2Eggs isAmountOf Egg
2Eggs value 2
This way at least the number of predicates is constant this way.
A fourth approach: maybe misuse the possibility to upt a literal into the object and combine an amount and the reference to the object into the literal: PancakeRecipe1 use 2,Egg.
A fifth approach: can there be predicates at a predicate? For example PancakeRecipe1 use[amount 2] Egg?
Process steps, order
How can I express the order a pancake recipe with tripels? This would be an additional information at the predicate, I guess (if there may be any additional information at the predicate):
PancakeRecipe1 use[amount 2, order 1] Egg
PancakeRecipe1 use[amount 200, unit g, order 2] Flour
PancakeRecipe1 use[amount 200, unit ml, order 3] Flour
Process steps, conditions
What is the triple expression for "Use either butter or margarine"?
Time dependent statements
How can a Semantic Web triple express chronological events or states? For example the amount of sold pancakes in a city (or maybe the more practical use case: the amount of citizens in a city in history)? There could be something like this:
Berlin soldPancakes2018 12345678
Berlin soldPancakes2019 14567890
Berlin soldPancakes2020 20123456
Or maybe Berlin soldObjects[object Pancake, periodFrom 2018-01-01, periodTo 2018-12-31] 12345678?
How is this expressable in RDF?
There are many subquestions not really related to the main question to fully answer each one of them. You also didn't specify whether you are looking for a particular vocabulary, or just for idea about transforming real-world entities into semantic triples. Let's say we are creating an ontology for the moment.
Process steps, amounts
A recipe is similar to a programming function: it has some ingredients (arguments) and steps (statements) to produce the result. You may want to describe them separately.
<recipe> :uses [
:product :egg ;
:minAmount 2
] .
Process steps, order
The individual steps can work in a similar manner, just in a list:
<recipe> :steps (
[
:action :break ;
:object [
:product :egg ;
:amount 2
] ;
:result _:x
]
[
:action :add ;
:object _:x
]
[
:action :add ;
:object [
:product :flour ;
:amount "200"^^:g
]
]
[
:action :mix
]
) .
Process steps, conditions
We can link from ingredients or steps to alternatives:
[
:action :add ;
:object [
:product :flour ;
:amount "200"^^:g
]
:alternative [
:action :add ;
:object [
:product :magicFlour ;
:amount "10"^^:g
]
]
]
As you can see, it is not hard to conceive a method for transforming ideas to triples that are sensible. What's hard is to find a consistent way for transforming all such sensible ideas to triples. Luckily, we are already covered by existing ontologies.
I find the RDFa Core Initial Context a useful place to check for recommended and common vocabularies. From there we can pick what is useful:
For describing complex time points or intervals, there is the Time Ontology.
Offers with a high degree of details can be described by GoodRelations.
For statistics and measurements, there are Data Cubes.
And lastly, Schema.org covers many real-world entities, including recipes.