I can't access the database schema of the reactome.db package:

> library("reactome.db")
> reactome_dbschema()

Warning messages:
1: In file(con, "r") :
  file("") only supports open = "w+" and open = "w+b": using the former
2: In max(ii) : no non-missing arguments to max; returning -Inf
> reactome_dbschema(show.indices=TRUE)

Warning message:
In file(con, "r") :
  file("") only supports open = "w+" and open = "w+b": using the former
#I found the following schema, but I can't read it 
> reactome_dbschema("R/x86_64-pc-linux-gnu-library/3.3/reactome.db/DBschemas/schemas_1.0/REACTOME_DB.sql")

Warning messages:
1: In file(con, "r") :
  file("") only supports open = "w+" and open = "w+b": using the former
2: In max(ii) : no non-missing arguments to max; returning -Inf
# And it doesn't seem to be up to date:
> con <- reactome_dbconn()
> query <- "SELECT COUNT(DISTINCT reactome_id) AS total_react FROM pathway2gene"
> res <- dbGetQuery(con, query)
Error in rsqlite_send_query(conn@ptr, statement) :
  no such column: reactome_id
# I could retrieve the actual schema by using the following:
> a <- dbGetQuery(con, "select * from sqlite_master")
# Which shows that the name of the columns has changed
> a[a$name == "pathway2gene", ]
     type         name     tbl_name rootpage
761 table pathway2gene pathway2gene  2173887
                                                                                                                                                                 sql
761 CREATE TABLE pathway2gene (\n  DB_ID VARCHAR(10) NOT NULL,                  -- Reactome DB_ID\n  gene_id VARCHAR(10) NOT NULL                  -- Entrez Gene\n)
> sessionInfo()

R version 3.3.2 (2016-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 14.04.5 LTS

locale:
[1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C            
[3] LC_TIME=es_ES.UTF-8        LC_COLLATE=en_US.UTF-8  
[5] LC_MONETARY=es_ES.UTF-8    LC_MESSAGES=en_US.UTF-8 
[7] LC_PAPER=es_ES.UTF-8       LC_NAME=C               
[9] LC_ADDRESS=C               LC_TELEPHONE=C          
[11] LC_MEASUREMENT=es_ES.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] parallel  stats4    stats     graphics  grDevices utils     datasets
[8] methods   base     

other attached packages:
[1] reactome.db_1.58.0   AnnotationDbi_1.36.1 IRanges_2.8.1     
[4] S4Vectors_0.12.1     Biobase_2.34.0       BiocGenerics_0.20.0
[7] BiocInstaller_1.24.0

loaded via a namespace (and not attached):
[1] DBI_0.5-1     tools_3.3.2   memoise_1.0.0 Rcpp_0.12.9   RSQLite_1.1-2
[6] digest_0.6.11

I think you have actually answered your own question. And actually found a bug. :)

To get the current schema you are probably better off using sqlite (and then the .schema command) directly on the sqlite file.

A while ago the schema was changed, and apparently, I did not update it in the package.
Currently, this package is developed in a two pronged way.
I create the mappings, and Valerie adds the full database dump.

There are too many half-manual steps at the moment, and it was already on my todo list to combine all the steps and to make sure we can automate this as much as possible. I will also add a test to check if the schema definition is current.