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Global analyses of Parton Distribution Functions (PDFs) have provided
incisive constraints on the up and down quark components of the proton,
but constraining the other flavor degrees of freedom is more challenging.
Higher-order theory predictions and new data sets have contributed
to recent improvements. Despite these efforts, the strange quark PDF
has a sizable uncertainty, particularly in the small x region.
We examine the constraints from experiment and theory, and investigate
the impact of this uncertainty on LHC observables. In particular,
we study W/Z production to see how the s-quark uncertainty propagates
to these observables, and examine the extent to which precise measurements
at the LHC can provide additional information on the proton flavor
structure. We then discuss the theoretical treatment of heavy quarks
in perturbative QCD and hence in global analyses. We discuss experimental
constraints on the charm quark PDF and propose ways how to find or
constrain a possible non-perturbative intrinsic charm/bottom distribution in the