Manchester United  manager Sir Alex Ferguson  says he has already identified his summer transfer targets, and has begun work on strengthening his squad ahead of next season.The 71-year-old believes Manchester United have a solid foundation to their squad but says the club will again try to be competitive in the transfer market after landing Robin van Persie and Shinji Kagawa last summer.The Scot wants to compliment his young talent, who will mature over the next few years, with additional quality to help United retain their title against challenges from big spending Manchester City and Chelsea."Hopefully the players we bring into the club in the next year or so will be of the quality we need," Sir Alex told the club's official magazine. "We're competitive in the market - we're not Chelsea or Manchester City in terms of money but we're competitive."We've been doing a bit of work on that over the last three or four months, targeting who the players are that we feel could enhance us, make us better or help us maintain the level we're at."You have to look at the structure of the club at present, in terms of the number of first-team players we have at 23 or under."David De Gea, Rafael, Phil Jones, Chris Smalling, Alex Buttner, Nick Powell, Tom Cleverley and Danny Welbeck. Shinji Kagawa and Chicharito are 24. Jonny Evans is 25 and Wayne Rooney is hitting his peak at 27."Older players like Ryan Giggs, Paul Scholes and Rio Ferdinand may be coming towards the end of their careers, but these younger players are the foundation for the next five or six years, irrespective of the players breaking through, like Adnan Januzaj, the Belgian boy, who's really looking very good."