Q: what to do with "iPhoto Events" inside Photos ?

iPhoto in Photos shows under Albums as "iPhoto Events".

Are all photos in iPhoto Events are aliases ?

Can "iPhoto Events" be deleted ?

The "iPhoto Events" are just albums, referencing the photos in your Moments.

Photos created an album for each of the events in your iPhoto Library to preserve your event structure. They do not need much extra storage. If you do not need the old event structure and did to invest much work into naming and organising the events in iPhoto, you can delete these albums or the folder "iPhoto Events" with all albums.

You can't remove photos from any system created album such as All Photos or from the Photos timeline without removing it from all albums. You can only remove it from user created albums without it deleting from the Photos Library.

If the dialogue say Delete Photo, then it will be completely deleted. If it says Remove From Album, the it will only be removed from that album.

So ALL of  "iPhoto Events" should exist in Photos as Albums ?

The iphoto events are regular albums and just use the photos in the Photos Library. Remove any album or remove photos from an album, and the phot will remain in the library.

If you use the "Photos" view a the top of the sidebar, you will see the Photos Library - structured in Moments, Collections, Years. These are the basic containers of the library.  Each photo will appear in exactly one Moment, just like iPhoto's events used to work. Delete a photo from a moment moment, and it will be removed from all albums, products, smart albums that are using this photo.

Albums and smart albums can be deleted without removing photos from the library. The photos will remain in their moments.

What confuses me and others is having "iPhoto Events" in Photos. I think it was Apple's mistake to leave the name 'iPhoto Events'.

The name is really not well chosen.   A more precise name, like "Simulated iPhoto Event Albums" would have been more appropriate. Even for my migrated Aperture Libraries this folder is called "iPhoto Events" and not "Aperture Projects".

. From now on I'll be peacefully waiting for big update.

I hope, we will not have to wait too long

i wonder if you can help with this question

i had made smart albums in iPhoto using filename and events

now the library is in photo, the events are visible as a smart album themselves, but all the smart albums i made are now 'modified' i.e. empty

what do you think?

the events are visible as a smart album themselves

The existing Events in iPhoto get converted to regular albums when migrated to Photos, not smart albums.

As for the empty smart albums, check what the criteria is because not all criteria that was available in iPhoto is available in Photos.  Missing criteria will result in empty smart albums.

Smart Albums did not transfer. You may have those album titles, but they are probably converted to regular album folders now. Since smart albums never really contained any photos, only criteria that pointed to photos, the albums are empty in Photos.

Your photos should have transferred. You will have to recreate the smart albums using the criteria you had before. You may have to check the criteria on the photos in the main library to make sure the criteria you set in iPhoto (such as name, keywords, etc) have also been transferred properly.

Have a look at this support document:   How Photos handles content and metadata from iPhoto and Aperture - Apple Support

Not all smart albums can be transferred without problems.  If a smart album used metadata, that cannot be accessed in Photos, the smart album will be named with a (modified) in the title and may be empty.  Since Photos does not support events, all smart albums referring to events will not work. Replace the missing constraint in the smart album by a rule that references the corresponding album in "iPhoto Events".

Thank you very much, it is so disappointing as i had spent a long time making the smart albums, but i will remake them

Many thanks for your replies

And all this time I didn't think any smart albums would transfer from iPhoto to Photos. None of mine did and if they would have, most should have worked. Maybe the conversion process is better than the first release of Photos.

My smart albums based on keywords worked well, but all smart albums referring events, camera make, ratings were a mess.

I had to replace the event names by date ranges.  It helped a lot to have iPhoto up and running, so I could see the original definitions of the smart albums.