add better document model for cassandra
add better document model for cassandra

mehanig/scrapi,mehanig/scrapi,fabianvf/scrapi,erinspace/scrapi,icereval/scrapi,CenterForOpenScience/scrapi,CenterForOpenScience/scrapi,felliott/scrapi,felliott/scrapi,ostwald/scrapi,erinspace/scrapi,alexgarciac/scrapi,jeffreyliu3230/scrapi,fabianvf/scrapi