Want to implement advanced search with more than one same type filter at a time in dspace 4.x XMLUI

I am using dspace 4.x XMLUI version. I want to add advanced search box in dspace like above,where we can search items of more than one "Type of Learning Material" at a time. For this purpose we have to generate 'OR' query. In dspace 4.x version,when we are searching using filter,a URL is generating in address bar,where all query filter is added using '&'. But in this case we have to generate two types of conjunction(&,OR). But I can't understand how to do it? I just find one clue that there has a file AdvancedSearch.java , where conjunctions are defined. But how can i implement this? Please help.