Expand empty sections and add advanced queries in episode 5 (closes #93)

episodes/05-intro_to_querying.md

@@ -122,6 +122,20 @@ SELECT * WHERE {
 
 ### Showing labels to Q-numbers
 
+By default, SPARQL queries return Q-numbers instead of human-readable 
+labels. To show labels, add the `SERVICE wikibase:label` block to your 
+query:
+
+```
+SELECT ?item ?itemLabel
+WHERE {
+?item wdt:P31 wd:Q7075.
+SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
+}
+```
+The `[AUTO_LANGUAGE]` placeholder automatically uses your browser's 
+language setting, with English as a fallback.
+
 ### Namespaces and Prefixes
 
 Prefixes are short abbrevations in the Wikidata Query Service. Some prefixes in Wikidata are: wd, wdt, p, ps, bd, etc.
@@ -148,11 +162,26 @@ Namespaces in Wikidata are:
 
 ### More conditions
 
-- publications from Addison-Wesley vs. books from Addison-Wesley vs. books authored by Richard Feynman from Addison-Wesley
-- LIMIT
-- ORDER
-- FILTER
-- OPTIONAL
+### More conditions
+
+You can combine multiple conditions in a single query. Here is an example 
+that finds books published by Addison-Wesley authored by Richard Feynman:
+
+```
+SELECT ?book ?bookLabel WHERE {
+?book wdt:P31 wd:Q571.        # instance of book
+?book wdt:P123 wd:Q353060.    # published by Addison-Wesley
+?book wdt:P50 wd:Q39246.      # authored by Richard Feynman
+SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
+}
+```
+Useful modifiers:
+
+- `LIMIT 10` — restrict results to 10 rows
+- `ORDER BY DESC(?date)` — sort results by date, newest first
+- `FILTER(YEAR(?date) > 2000)` — filter by year
+- `OPTIONAL { ?item wdt:P18 ?image }` — include a field only if it exists
+
 
 ### How to visualize your query
 
@@ -552,13 +581,44 @@ WHERE
 
 ## 5\.4 More Advanced queries
 
-further links
+Here are some more advanced query patterns that are particularly useful 
+for library use cases.
+
+### Federated queries and subqueries
 
+You can use subqueries to pre-filter data before the main query processes 
+it, which can significantly speed up complex queries:
+
+```
+SELECT ?item ?itemLabel ?authorLabel WHERE {
+?item wdt:P31 wd:Q13442814.     # scholarly article
+?item wdt:P50 ?author.
+?author wdt:P108 wd:Q49210.     # affiliated with a specific institution
+SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
+}
+LIMIT 20
 ```
-https://commons.wikimedia.org/wiki/File:Wikidata_Query_Service_in_Brief.pdf
-https://www.uni-mannheim.de/media/Einrichtungen/dws/Files_Teaching/Semantic_Web_Technologies/SWT05-SPARQL-v1.pdf
-https://www.wikidata.org/wiki/Wikidata:SPARQL_tutorial
+### Maintenance queries
+
+Maintenance queries help identify items that are missing information. 
+These are useful for librarians who want to improve data quality:
+
 ```
+# Libraries without coordinates
+SELECT ?item ?itemLabel WHERE { ?item wdt:P31 wd:Q7075. # instance of library FILTER NOT EXISTS { ?item wdt:P625 ?coord } SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". } } LIMIT 20
+```
+
+```
+# Scholarly articles without a DOI
+SELECT ?item ?itemLabel WHERE { ?item wdt:P31 wd:Q13442814. # scholarly article FILTER NOT EXISTS { ?item wdt:P356 ?doi } SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". } } LIMIT 20
+```
+
+### Further resources
+
+- [Wikidata Query Service in Brief (PDF)](https://commons.wikimedia.org/wiki/File:Wikidata_Query_Service_in_Brief.pdf)
+- [SPARQL tutorial on Wikidata](https://www.wikidata.org/wiki/Wikidata:SPARQL_tutorial)
+- [SPARQL lecture slides, University of Mannheim](https://www.uni-mannheim.de/media/Einrichtungen/dws/Files_Teaching/Semantic_Web_Technologies/SWT05-SPARQL-v1.pdf)
+
 
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