# Annotation parameters - AnnotParam

The __AnnotParam__ class is meant to store the minimal set of information 
necessary to retrieve the annotation

The minimal information to provide is:

1. a datasource: a path to a file provided as a character string or if the _type_
is biomaRt, the datasource you want to connect to, as retrieved using the
__biomaRt__ __datasource__ function.
2. a type: one of "gff3","gtf","rda", and "biomaRt". _gff3_ is the default. If 
_rda_ is used, it expects the corresponding file to contain a _GRanges_ object
by the name of _gAnnot_.

In this tutorial, we will reproduce the analysis performed in _Robinson, 
Delhomme et al._ [@Robinson:2014p6362]. For that we will start by downloading
the original annotation gff3 file for _P. trichocarpa_, a close related species
of the trees used in the study into the current directory. 

```{r P trichocarpa annotation}
download.file(url=paste0("ftp://ftp.plantgenie.org/Data/PopGenIE/",
                         "Populus_trichocarpa/v3.0/v10.1/GFF3/",
                         "Ptrichocarpa_210_v3.0_gene_exons.gff3.gz"),
                  destfile=,"./Ptrichocarpa_210_v3.0_gene_exons.gff3.gz")
```

Before instantiating an "AnnotParam" object.

```{r AnnotParam}
    annotParam <- AnnotParam(
        datasource="./Ptrichocarpa_210_v3.0_gene_exons.gff3.gz")
```

This annotation file however contains multiple copy of the same exons, _i.e._ 
when exons are shared by several isoforms of a gene. This might result in 
so-called "multiple-counting" and as described in these guidelines[^1], we 
will to circumvent that issue create a set of synthetic transcripts.

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