Below is the relational schema for which I have to write Relational algebra queries. The tables are also pasted.

region(region_id, region_name)

grape_variety(variety_id, variety)

wine(wine_id, wine_name, wine_type, year, winery_id)

winery(winery_id, winery_name, region_id)

wine_type(wine_type_id, wine_type)

wine_variety(wine_id, variety_id, id)

1. List the name of the wineries that produce fortified wines.

2. List the names of the wines and the name of the winery that produces a white wine from the Riverland region.

3. List the names of all wineries that make Gris wine, but do not make Shiraz wine.

region table:

region_id	region_name
1	'All'
2	'Goulburn Valley'
3	'Rutherglen'
4	'Coonawarra'
5	'Upper Hunter Valley'
6	'Lower Hunter Valley'
7	'Barossa Valley'
8	'Riverland'
9	'Margaret River'
10	'Swan Valley'

grape_variety

variety_id	variety
1	'Riesling'
2	'Chardonnay'
3	'Sauvignon'
4	'Blanc'
5	'Semillon'
6	'Pinot'
7	'Gris'
8	'Verdelho'
9	'Grenache'
10	'Noir'
11	'Cabernet'
12	'Shiraz'
13	'Merlot'
14	'Dessert'
15	'Muscat'
16	'Sherry'
17	'Port'
18	'Champagne'
19	'Sparkling'
20	'Red'
21	'White'

wine

wine_id	wine_name	wine_type	Year	winery_id
1	'Archibald'	2	1997	1
2	'Pattendon'	3	1975	1
3	'Lombardi'	4	1985	2
4	'Tonkin'	2	1984	2
5	'Sears'	5	1986	2
6	'Serrong'	6	1995	2
7	'Mettaxus'	5	1996	2
8	'Sears'	4	1987	6
9	'Serrong'	3	1981	6
10	'Chester'	5	1999	7
11	Chemnis	2	1980	8
12	Holdenson	6	1979	9
13	Skerry	2	1975	10
14	Sears	5	1978	11

winery

winery_id	winery_name	region_id
1	'Hanshaw Estates Winery'	2
2	'De Morton and Sons Wines'	8
3	'Joness Premium Wines'	3
4	'Borg Daze Premium Wines'	5
5	'Binns Group'	6
6	'Davie Brook Vineyard'	3
7	'Eglington Creek Premium Wines'	4
8	'McKay Station Vineyard'	4
9	'Dennis and Sons Wines'	5
10	'Beard Brothers Vineyard'	8
11	'Rowley Brook Group'	8

wine_type

wine_type_id	wine_type
1	'All'
2	'Sparkling'
3	'Fortified'
4	'Sweet'
5	'White'
6	'Red'

wine_variety

wine_id	variety_id	id
1	19	1
1	20	2
2	16	1
3	14	1
4	18	1
5	5	1
5	3	2
5	4	3
6	12	1
6	11	2
7	6	1
7	7	2
8	14	1
9	16	1
10	2	1
11	18	1
12	11	1
12	13	2
13	12	1
13	21	2
14	7	1