Automated Extraction of Data from Binary Phase Diagrams 7
represent the information from the graphic include annotations, effort, words
in caption, and highlighted components. Allen et. al [16], in one of the earliest
works in the area developed a system for deducing the intended meaning of an
indirect speech act. In [9], a similar idea is used in understanding line plots by
breaking down each line plot into trends and representing each trend by a mes-
sage. These constituent trend level messages are combined to obtain a holistic
message for the line plot.
While phase diagrams belong broadly to the class of plots, they require spe-
cial treatment due to the complex embedding of information into these diagrams,
as explained in the next section. The contour nature of the plot, complex text
placement with semantic import, and challenging locations and orientations cou-
pled with the optional presence of other graphic symbols such as arrows that are
vital for semantic interpretation of the figure, justify a dedicated exploration of
such complex diagrams.
3 Phase Diagrams
Phase diagrams are graphs that are used to show the physical conditions (tem-
perature, pressure, composition) at which thermodynamically distinct phases
occur and coexist in materials of interest [17]. A common component in phase
diagrams is lines which denote the physical conditions in which two or more
phases coexist in equilibrium - these are known as phase boundaries. The X and
Y axes of a phase diagram typically denote a physical quantity such as temper-
ature, pressure and, in the case of alloys or mixtures, the ratio of components
by weight or by molar fraction. As stated earlier, we focus on phase diagrams of
binary metal alloys where the X-axis is molar fraction percentage and the Y axis
is temperature. In Fig. 1, the blue lines within the plot denote the phase bound-
aries. All points bounded by a phase boundary represent physical conditions at
which the material of interest, in this case an alloy of silver and zinc, occurs
in the same phase. The name or label of this phase, for example α in Fig. 1,
is typically present somewhere within the phase boundary. The various Greek
letters present in the phase diagram represent different types of solid phases (i.e.
crystal structures). Positioning within a phase defines the ratio of the different
phases, as well as the composition of the phases. All of these characteristics
heavily impact the material properties.
We can observe that there are several regions that are unlabeled. These
regions represent multi-phase regions and the phases that constitute this mixture
are obtained by using the phase labels of the regions to the left and right of the
unlabeled region. Additionally, as shown in Fig. 2, in several phase diagrams,
labels are sometimes provided to the phase boundary instead of the region.
These cases represent intermetallic compositions (ie. the labeled phase exists
only at that one composition, thus explaining the vertical line which is labeled).
In such cases, the same rule to infer phase labels holds true except we would be
using a vertical line on the left or on the right to obtain one of the two phase
labels.