Core Data model design — search vs relationships?
I'm familiar with Core Data basics and have done some dabbling, but have not really done any major apps. Now I need to plan for one. And the question is not specifically about Core Data, but more about data design in general, though I am going to use Core Data to implement it on iPhone which is important for considering performance.

Imagine I am making an email app, where emails are the core object. I need to provide multiple views into the email store: search by user as well as many other criteria: say, "all emails with more than two recipients", "all emails where subject is longer than X", "all emails containing word X" etc.

Some objects, like people (senders/recipients), lend themselves naturally to being modeled as first-class objects, so I could do that and just create many-to-many relations between people and emails. Other searches, such as some examples above, are more artificial and there is no natural way to model them. However, I am able to enumerate the new searches in advance, i.e I know beforehand what will be the criteria.

So, to do things like "emails with >2 recipients" and "emails where subject is longer than X", I think I have two strategies:

1) model these as a special "search" object, and create many-to-many relations between emails and search objects when inserting new objects into store so it is a simple join query when searching;

2) not model anything beyond the core email object and just do searches with predicates from the store at runtime.

My question is:

based on your Core Data instincts, how big is the difference between these two strategies from a performance perspective? My gut tells me #1 will always be faster, but if it is 10%, I am willing to take the performance hit in order to be more flexible with #2. But if #2 will be 200% slower, I need to put more work into modeling the search object and essentially pre-generating all the search results.

I know the exact answer will depend on specifics of data, but there must be a gut feeling you have :) Let's say there are on the order of tens of thousands, but not millions, of content objects, and each record is a few paragraphs of content text with several fields of metadata.
Core Data model design — search vs relationships?
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I'm familiar with Core Data basics and have done some dabbling, but have not really done any major apps. Now I need to plan for one. And the question is not specifically about Core Data, but more about data design in general, though I am going to use Core Data to implement it on iPhone which is important for considering performance.

Imagine I am making an email app, where emails are the core object. I need to provide multiple views into the email store: search by user as well as many other criteria: say, "all emails with more than two recipients", "all emails where subject is longer than X", "all emails containing word X" etc.

Some objects, like people (senders/recipients), lend themselves naturally to being modeled as first-class objects, so I could do that and just create many-to-many relations between people and emails. Other searches, such as some examples above, are more artificial and there is no natural way to model them. However, I am able to enumerate the new searches in advance, i.e I know beforehand what will be the criteria.

So, to do things like "emails with >2 recipients" and "emails where subject is longer than X", I think I have two strategies:

1) model these as a special "search" object, and create many-to-many relations between emails and search objects when inserting new objects into store so it is a simple join query when searching;

2) not model anything beyond the core email object and just do searches with predicates from the store at runtime.

My question is:

based on your Core Data instincts, how big is the difference between these two strategies from a performance perspective? My gut tells me #1 will always be faster, but if it is 10%, I am willing to take the performance hit in order to be more flexible with #2. But if #2 will be 200% slower, I need to put more work into modeling the search object and essentially pre-generating all the search results.

I know the exact answer will depend on specifics of data, but there must be a gut feeling you have :) Let's say there are on the order of tens of thousands, but not millions, of content objects, and each record is a few paragraphs of content text with several fields of metadata.