What sort of advice are you after?

Irrigation?
Plants?

Do you happen to have a picture or two so that we can visualise it? I am pretty sure it won't be like anything we have here in the UK

I live in a climate just like this, and so do one or two other people on this site. Rosemary and Lavender will pretty much look after themselves once they are well established, and I doubt they really need any sort of irrigation system. They are also pretty hardy, so your freezing winters and scorching summers won't be a problem for them, or for thyme or sage. You could also try planting bearded irises, which are pretty hardy and I never bother too much about watering mine. Oleanders seem to work quite well, and hardy succulents like sempervivums and perennial Livingstone daisies (forgotten the proper name for these - not Mesembryanthemum, they die overwinter)
I have never had any kind of irrigation system (except for my Other Half with a hosepipe), but then, we live here year round. I believe they can be very expensive and don't work that well, so do your homework carefully! We tend to use water only where we are growing fruit and vegetables, and if you can choose carefully, you should be able to keep some sort of ornamental planting going throughout the year. Don't plant in pots! Despite fiercely freezing winters, we have two olive trees and lots of fig trees that seem to survive better than most people would give them credit for, but again, they do need some sort of protection until they are well established.
I shall be really interested to see what other people suggest.

I'm in Spain (north), but, like Gattina, live here year round so don't have any problem with watering. I can only agree with the plants Gattina has mentioned which require little water and are hardy once established. It'll be the weeds that will drive you bonkers!

Thank you so much for your answers. The house is a traditional four sided Northern Spain house built around a central patio area. This inner patio is just compacted stone and dirt, it was once a farmyard. This will be a gravel garden with large planters which I wish to plant up with lavenders and herbs, and maybe alpines in the gravel. Do I use ordinary compost of some kind of mixture? (I am by no means a gardening expert). I think they will all certainly need to to be irrigated in the summer. Do you agree?
The garden outside the patio is laid to lawn with a stream running alongside the back of the house. There is a neighbours wall at the back of the garden where the soil stays quite moist as he waters his own garden when it is hot! This is where I will put a border of shrubs. These I will take over from England (there are very few garden centres there).I think it is a bit hit and miss whether they will all do well.
There is an old fig tree there and several pears which all produce masses of fruit. Wish me luck!

I think a lot of us with gardens in hot/cold climates fill them with the products from British garden centres, Ann. Like Spain, Italy does not have the same gardening culture, and specific plants and products are sometimes hard to find.
I think attempting to maintain a lawn is going to be a non-starter unless you can get your neighbour to water and mow it for you while you aren't there. Who will feed it? Weed it? Clip the edges? I think it would give you a lot of problems, as would planting in containers. These allow roots to freeze in winter and cook in summer, and can never catch enough rain to keep things alive. They may look extremely beautiful, but they are not the ideal situation for any plant. Be aware that weeds will be a big problem, and you'll possibly spend your precious holidays armed with gardening gloves and a weeding fork. Do you let out the house when you aren't there?
One thing I forgot to recommend before was ROSES! These should do well even in extremes of temperature, and are very forgiving on the watering front if you choose wisely. I'm no expert, so I couldn't advise which varieties would do best, but I'm sure there's someone who could.....
Yes, I certainly wish you luck! I think you may need it! Let us know how you get on.