diff --git a/available.go b/available.go
index a34d8ae..6cd400e 100644
--- a/available.go
+++ b/available.go
@@ -1,8 +1,10 @@
 package pm
 
 import (
+	"fmt"
 	"net/url"
 	"sort"
+	"strings"
 
 	"github.com/pkg/errors"
 )
@@ -28,10 +30,52 @@ func (v Versions) Len() int           { return len(v) }
 func (v Versions) Swap(a, b int)      { v[a], v[b] = v[b], v[a] }
 func (v Versions) Less(a, b int) bool { return v[a] < v[b] }
 
+type label struct {
+	n Name
+	v Version
+}
+
+type labels []label
+
+// TODO (sm): make this semver sort?
+func (n labels) Len() int      { return len(n) }
+func (n labels) Swap(a, b int) { n[a], n[b] = n[b], n[a] }
+func (n labels) Less(a, b int) bool {
+	if n[a].n != n[b].n {
+		return n[a].n < n[b].n
+	}
+	return n[a].v < n[b].v
+}
+
 // Available is the structure used to represent the collection of all packages
 // that can be installed.
 type Available map[Name]map[Version]Meta
 
+// Get returns the meta stored at a[n][v] or an error explaining why it could
+// not be Get.
+func (a Available) Get(n Name, v Version) (Meta, error) {
+	if _, ok := a[n]; !ok {
+		return Meta{}, errors.Errorf("could not find package named %q", n)
+	}
+
+	if v == "" {
+		if len(a[n]) == 0 {
+			return Meta{}, errors.Errorf("no configured versions for %q", n)
+		}
+		vers := Versions{}
+		for ver := range a[n] {
+			vers = append(vers, ver)
+		}
+		sort.Sort(vers)
+		v = vers[len(vers)-1]
+	}
+
+	if _, ok := a[n][v]; !ok {
+		return Meta{}, errors.Errorf("could not find %v@%v in database", n, v)
+	}
+	return a[n][v], nil
+}
+
 // Add inserts m into a.
 func (a Available) Add(m Meta) error {
 	if _, err := m.Valid(); err != nil {
@@ -92,3 +136,52 @@ func (a Available) Traverse() <-chan Meta {
 	}()
 	return r
 }
+
+func labelForString(s string) (label, error) {
+	r := label{}
+	c := strings.Count(s, "@")
+	switch c {
+	case 0:
+		r.n = Name(s)
+	case 1:
+		sp := strings.Split(s, "@")
+		r.n, r.v = Name(sp[0]), Version(sp[1])
+	default:
+		return r, fmt.Errorf("unexpected number of '@' found, got %v, want 1", c)
+	}
+	if r.n == "" {
+		return r, fmt.Errorf("name cannot be empty")
+	}
+	return r, nil
+}
+
+// Installable calculates if the packages requested in "in" can be installed.
+func (a Available) Installable(in []string) (Metas, error) {
+	ls := labels{}
+	for _, i := range in {
+		l, err := labelForString(i)
+		if err != nil {
+			return nil, errors.Wrap(err, "parsing name/version")
+		}
+		ls = append(ls, l)
+	}
+
+	seen := map[Name]bool{}
+	for _, l := range ls {
+		if _, ok := seen[l.n]; ok {
+			return nil, fmt.Errorf("can only ask to install %q once", l.n)
+		}
+		seen[l.n] = true
+	}
+
+	ms := Metas{}
+	for _, l := range ls {
+		m, err := a.Get(l.n, l.v)
+		if err != nil {
+			return ms, errors.Wrapf(err, "getting %v", l)
+		}
+		ms = append(ms, m)
+	}
+
+	return ms, nil
+}
diff --git a/meta.go b/meta.go
index a4d9ace..1ba591a 100644
--- a/meta.go
+++ b/meta.go
@@ -27,3 +27,6 @@ func (m *Meta) Valid() (bool, error) {
 	}
 	return true, nil
 }
+
+// Metas is a slice of Meta
+type Metas []Meta