Take a look at an example database schema below

Publication (pubID, title, year, description, typeID, subjID, staffID) Staff (staffID, first_name, last_name, email_address) Editor (editorID, first_name, last_name, email_address) Author (authorID, first_name, last_name, email_address) Type (typeID, type_name, description) Subject (subjID, subject_name, description) AuthorEditor (authorID, editorID) EditorPublication (editorID, pubID) AuthorPublication (authorID, pubID)

Make a Relational Algebra to find the authors name who wrote all Journal type publication in specific subject about Energy & Power.