Computer Associates, one of the world's largest software companies, has agreed to acquire Sterling Software for $4 billion. The business software specialist said the acquisition of Sterling would help expand its range of products. Sterling will add portal software to CA's stable of products. The software provides access to corporate databases and enterprise application integration tools, software that allows various business applications to communicate. Under the agreement, CA will offer to exchange 0.56 shares of its stock for each outstanding Sterling share. CA, which employs more than 40 people in Ballsbridge, said it now plans to combine Sterling's products with its own technology, including its intelligent Neugents neural network software.