Hundreds of small, independent publishers will have easier access to digital book technology under a new service offered by Perseus Books Group, the result of agreements between it and more than a half-dozen technology companies, Perseus is expected to announce on Thursday.The new service, called Constellation, will allow independent publishers to make use of electronic readers, digital book search, print-on-demand and other digital formats at rates negotiated by Perseus on their behalf. Unlike large publishers, small ones typically lack the resources to use digital technology and as a result often bypass it altogether.