Blog site common approach, display short version of post and full versionn

[Ownetateecync]

I'm trying to develop web application (php/mysql), sort of blog site where ~10 posts are listed on front page. Only first 4-5 lines of each post are displayed and when user clicks the title it opens new page with full post displayed.Users will use TinyMCE to post with very limited functionality, so bold, italics, underline, undo/redo and bullet lists only. No HTML view, no links nor images so nothing fancy.Now, as two displays of the same posts are involved, so the one on front page where part is displayed only, and full version, I'm not sure if I should:

• when user submits post I should clear it up with something like HTMLPurifier and store one full version in database. Then cut first 4-5 lines of it, and clear it with HTMLPurifier again to make sure all tags are closed properly. This is to make sure the text I cut doesn't finish with html tag cut in half but rather is valid (x)html properly closed. I would store this shorten front-page version somewhere in database again. So I would have two versions in database ready, full post version and shorten front-page version. Then when someone accesses the site and displays front page with 10 posts, these just need to be read from database and displayed. No need for reading full version, cutting the top of it, making sure all tags are properly closed etc. etc. for all 10 posts every time someone opens the site. The obvious problem would seem that part of content is doubled in database so full version and short version.
• Another option I thought about would be when user submits post, clear it up with HTMLPurifier, and store only full version to database. Then when someone accesses the site, cut top part of each blog post, clear it up with HTML purifier (again!) to make sure its all valid, tags are closed etc. and display on front page. Now the problem seems that HTMLPurifier would have to be run and clean every single time when someone accesses the short version of the post, so e.g. 10x for frontage for each visit and so on.

I used HTMLPurifier above as an example only as I'm sure there are other tools douing same thing so please advice if anything else would be more appropriate in my situation. Also I will probably allow users to display more than 10 posts per page.Ok, I'm sure there is some common pattern to deal with this sort of site and if so please give me an idea of how it should be done as my thought above seems to have many obvious problems. As always your help is much appreciated.EDIT: I should have clarified.. Its more like an exercise to me and I wanted to learn how this sort of site should be done. Same concept can be implemented on other sites so advertising, forums etc. anything with posting really. For blogging I sure could use something ready but this time I wanted to learn.