Editor's Note: This is the fourth of a series of posts excerpted from Jason Griffey's Library Technology Report "3D Printers for Libraries."
As noted in earlier posts in the series, FDM (fused depostion modeling) printing is by far the most common inexpensive method of 3D printing. In this post, we’ll look at alternatives.
We are starting to see stereolithography (SLA) printing move downmarket into the affordable-for-libraries zone. I’m aware of a couple of libraries that have already purchased stereolithography printers.
SLA involves a light-sensitive resin and lasers. Liquid resin is contained in the body of the printer, with a build plate that moves up and down inside the resin. The resin solidifies when exposed to a specific wavelength of light, usually in the UV spectrum, and the printer has a laser or lasers tuned to that specific wavelength. The build plate starts near the top of the resin, and the lasers sweep across, solidifying the resin in the appropriate areas. The build plate then lowers, and the lasers repeat their sweep, building layer after layer, one after the other as the object is built. You can also have this process occur upside down, as in the FormLabs Form 1 printer, where the build plate is actually above the resin, and as layers are added it pulls the completed layer out of the resin.
SLA printing has several advantages over FDM. Because the print is always encased in liquid resin during the process, it is much more forgiving as to geometry of design. Not completely-- there still has to be some connection to the base layer. You couldn’t print a “floating” horizontal piece, for instance. But in general, the resin provides substantially more support for designs than those available from FDM printers. The other major advantage is that the detail level is limited by the crystallization of the liquid and the size of the lasers, which means that you can have very fine details in an SLA print. It’s possible to achieve .025mm (25 microns) layer heights with SLA prints.
Stereolithography printing has its limitations. The first is that the resin is only available in a very limited number of colors, generally a clear or translucent material and white. When compared to the rainbow of colors available for FDM printing with ABS or PLA, it feels limiting. The second, and far more worrisome, is that most vendors of this type of printer manufacture their own resin. The printers are designed to tune the wavelength of the lasers to the specific resin they sell, thus making it very difficult for anyone to compete with them on consumables for the printer. This would be the equivalent of buying a printer from HP, and having to then buy paper and toner from them as well in order to use the printer.
Small SLA printers are just beginning to hit the market, available in the $2,500-3,500 range. The consumable for printing, the photosensitive resin, is more expensive than filament for FDM printing as well. The most popular of consumer-grade SLA printers, the FormLabs Form 1, has resin that sells for $149 per liter.
Selective Laser Sintering
Simultaneously the most flexible and the most expensive type of 3D printing commonly used, selective laser sintering (SLS) printing is similar to stereolithography in that it uses lasers to solidify a loose substrate. In SLS printing, the printing substrate is a powder, and the printers use high-energy lasers, rather than UV. The high-energy lasers selectively fuse sections of a powder together, a new layer of powder is deposited on top of the sintered layer as the entire print bed drops, and the lasers do another pass, fusing the single-layer of powder to the already solid layer below. Thus prints are completed layer by layer, exactly as in the other printing technologies that we covered, except the end product is a solid object that’s been drawn by lasers, encased in all of the powder that wasn’t fused.
This method provides total support for the print in question, so nearly any imaginable geometry can be printed using SLS printing. It is also possible to use any material for SLS that is capable of being powdered and fused with heat, including thermoplastics, covered in my previous post, as well as steel, aluminum, titanium, and other metals and alloys. Prints produced in this way are very nearly as strong as solid-cast parts, which means that it’s possible to 3D print mechanical parts that are directly usable in engineering projects via SLS printing.
Layer height and resolution in SLS printing is completely determined by the resolution of the powder being fused, but is typically on par with SLA printing, averaging around .1mm layer heights. Another similar technology is electron beam melting (EBM) that uses high energy electron beams to melt powdered metals in order to produce 3D objects. The use of electron beams allows for even higher precision than lasers, allowing for up to .05mm layer heights, which is nearly unheard of by any other method.
Laminated Object Manufacturing
The last specific type of 3D printing that I’ll describe is, in my opinion, particularly clever. Laminated Object Manufacturing takes thin materials like paper or plastic sheets, cuts them to a specific shape, and then uses adhesive to glue one layer to the next. The most well known of these types of printers is manufactured by a company called MCor Technologies. Their printer uses normal, ordinary copy paper as its substrate, cutting one sheet at a time into the appropriate shape for the given layer, and then using paper glue to laminate the individual layers together. The high-end model of the MCor printer includes a full-color inkjet printhead inside, to allow for full color 3D prints to be created from very inexpensive raw materials; literally paper, ink, and glue.
Other 3D Printing Types
Numerous other 3D printing technologies are available, many that are patented and limited to a single company. For example, 3D Systems uses a type of 3D printing methodology that they call Color-Jet Printing (CJP) that uses two different materials that are combined using a sort of high-end inkjet printer in order to create the solid end-product. This patented process allows them to print in materials like food-grade ceramic. 3D Systems also makes a 3D printer that is capable of printing in sugar, called the ChefJet, and the high-end model, the ChefJet Pro can print edible 3D models in full color.
Editor's Note: This is the third of a series of posts excerpted from Jason Griffey's Library Technology Report "3D Printers for Libraries."
The substrate for FDM printers are almost exclusively some form of thermoplastic that is delivered in an extruded wire-like form on a spool. It is usually called “filament” in the generic. The two common diameters for use in FDM printing are 1.75mm and 3mm, and a specific diameter is called for by the print head being used for the printer in question. A printer that uses 1.75mm diameter filament won’t be able to use 3mm without retrofitting the hardware for the difference, and vice versa. Slightly more common, the 1.75mm diameter is used by Makerbot Industries, the most popular manufacturer of FDM printers.
In later postss, when I write on the different printer types and manufacturers, I’ll note what type of filament they are capable of printing, because that turns out to be a major limitation and purchasing decision factor.
The original fused deposition printers almost exclusively used ABS (Acrylonitrile butadiene styrene) as their substrate for printing. ABS is nearly ideal from a material property point of view for rapid prototyping in plastic, as it’s strong, slightly flexible plastic, which extrudes cleanly at between 220° and 240° celsius. ABS is the type of plastic used in Lego bricks, and is one of the most commonly used industrial/commercial plastics.
For FDM printing, ABS requires a heated print bed to ease the thermal shock for printing. Heating the print build plate aids the plastic in both adhering to the plate for stability, and in preventing cooling too quickly, which leads to thermal deformation, or a sort of curling separation. ABS is sensitive enough in this arena that many people who print ABS learned early on that enclosing the printer was a way to increase the stability of prints because it regulated the temperature around the printer. I soon discovered in my printing experiments with an early Makerbot printer (Replicator 1) that even a strong breeze blowing in the wrong place (across the print bed) could wreak havoc. Higher end printers will have an enclosed print area, while less expensive ones don’t.One of the advantages of ABS is that it dissolves in acetone. Acetone dissolves ABS completely, but used sparingly it can act as a glue to fuse two ABS printed pieces together permanently. Acetone is also used to make a “glue” for print beds, to help in making the print bed sticky for the initial printed layers. Acetone vapor is heavier than air, and some people have used this to build acetone vapor baths that act to smooth the edges of layers of an FDM ABS print.ABS has caught some bad press recently, as the potential effects of off-gassing of the heated plastic and microparticulate effects are studied. As a petroleum based plastic, ABS does produce a distinctive stink when printing. Fumes have been reported to cause headaches, and studies link ABS fumes to olfactory loss; one study that found ABS printing released high volumes of ultrafine particles that could be dangerous when inhaled. These are preliminary studies. Most haven’t been repeated, and the science is still rough on the health effects here. But if you need to print with ABS, it may be a good idea to take venting into account.
PLA (Polylactic acid) is the second most popular printing substrate for FDM printers. A bioplastic, PLA is made from corn, beets, or potatoes. It is compostable in commercial compost facilities (the heat and bacterial action isn’t high enough in home composting to break it down). It melts at a much lower temperature than ABS (150-160°C), but is typically extruded at a higher temperature, anywhere from 180-220°C depending on the PLA itself. Because of it’s lower temperature, it’s not suitable for uses that involve high temperatures and direct sunlight. PLA is also very different than ABS in term of fragility. Far more crystaline, PLA shatters or cracks more readily than ABS, whih instead will deform under pressure.
However, Makerbot and other major manufacturers are now starting to go with PLA as their primary printing plastic. PLA doesn’t require a heated bed for adhesion or thermal curling reasons, which lowers the price of the printers that use it. As well, it’s far more thermally stable during printing than ABS, and much less likely to warp or curl due to errant breezes. It is possible to reliably print PLA without needing to enclose your printer, which can be a huge benefit in many circumstances.
The other significant advantage is that PLA is far more pleasant when printing than ABS. Because it is a bioplastic, when heated it smells like waffles or syrup, and not like an oil spill. It also hasn’t been linked to any types of medical issues from being heated, although the study of all these plastics is young when it comes to 3d printing specifically.
One of the other advantages of PLA is that it’s available in dozens and dozens of colors, including both opaque and partially transparent, as well as a couple of colors of glow-in-the-dark. It also is available in a flexible form, which can produce prints that are almost rubber-like in consistency.
If you are printing in a library setting, I would suggest focusing on PLA. Between the reliability and the ease of working with it, it’s a far better choice than ABS for printing in a public space.
Once you get beyond ABS and PLA, you’re in the realm of specialized plastics that are used for specific properties rather than for general 3D printing. More of these appear every day, practically, but generally they fall into a couple of categories: dissolvable support material, specific material qualities that are needed, or non-plastic powder suspended in a thermoplastic resin. I’ll describe the most common of these below.
High Impact Polystyrene or HIPS is a plastic filament used for dissolvable support structures in FDM printers. It extrudes at around 235°C and has a set of material properties that make it similar to ABS. The main difference is that HIPS is completely soluble in a liquid hydrocarbon called limonene. This means that if you have an FDM printer with more than one print head, you can extrude ABS from one and HIPS as a support material from the other, and sit the final printed model in a bath of Limonene. The HIPS will dissolve away, leaving only the ABS behind, thus allowing for nearly impossible geometries to be printed, including moving ball bearings and more.
There are at least 4 types of nylon currently available for use in FDM printers: Nylon 618, Nylon 645, Nylon 680 and Nylon 910. These vary in their color from medium transparency to fully opaque white, and all are extraordinarily strong as compared to other FDM substrates. They are also very resistant to solvents and such, although they are dyeable with acid-based dyes for coloring.
Nylon as an FDM printing material is more expensive than PLA or ABS. The major reason for using them would be for specific material properties (resistance to specific chemicals) or due to the need for FDA approved materials, as both Nylon 680 and 910 are undergoing FDA approval for use, something rare in the 3D printer world.
T-Glase is a brand name for a filament composed of Polyethylene terephthalate. Of all 3D printer filaments, it is the most glass-like. Nearly transparent, especially at small sizes, it could easily be mistaken for glass. At larger sizes it is still very light-transmissive, if not fully transparent. T-Glase prints at around 221°C, on a heated bed, but is very stable and resistant to curling.
LayBrick & LayWood
Another type of printing material for FDM printers, these fall squarely in the experimental realm. They are made by a single manufacturer, and are both a sort of hybrid filament, with a powdered material being supported inside a resin. In the case of LayWood, fine wood particles are suspended in a thermoplastic resin, and in the case of LayBrick, it would be very finely crushed chalk and other minerals suspended in the resin.
Both LayBrick and LayWood have the interesting property of variability in appearance depending on the temperature at which they are printed. LayBrick can range from a very smooth, almost ceramic feel, to very rough sandstone, just by increasing the heat of extrusion. For very smooth, you print at a low temperature (165°C to 190°C) and then going up from their to around 210°C will render the printed part more and more rough. For LayWood, the difference is in the appearance of the final product. By increasing the temperature, you get darker and darker wood grain from the output, so you can actually vary the look from light to dark wood (or, if you have a printer that supports variable temperatures during a single print, you can get different colors in a single print by varying the temperature).
One of the risks, however, with both of these is that the filament isn’t uniform in construction, which means that it’s possible to clog your extruder if the nozzle opening is smaller than the particulate in the filament itself. FDM printers nozzle openings range from .35 to .5mm, and on the lower end of that, especially with the LayWood (organic particles are harder to ensure regular sizes than inorganic particulate) you risk clogging a nozzle. I know 3D printers that have clogged even at .4mm nozzle using LayWood. For printing these sorts of filaments, the larger the nozzle the better.
Still very experimental, polypropylene (PP) offers the possibility of food-grade 3D prints. Polypropylene should work with any FDM printer, at an extrusion temperature of 201°C and a heated print bed set to 90°C. It looks like PP is only really available in black.
Challenges with Fused Deposition Modeling
Most of the issues with FDM printing are related to the fact that it’s a very mechanical process, and tuning the printer is key. The most sensitive aspect of the process is the relationship between the extruder and the build plate. Because the printhead has to extrude an even layer of plastic onto the build plate, it’s necessary that the build plate be perfectly flat relative to the nozzle. If there is any warp or uneven-ness, you’ll get uneven attachment to the plate or other forms of print failure. This is the most common issue with FDM printing, especially with new operators. The first question to ask if a print fails is: “Is my build plate level/”
And prints will fail. FDM printing is a complicated mechanical process, and while you can tune a FDM printer to be very reliable, at some point you will have a failure and will come back to a print that looks like someone poured plastic spaghetti on your build plate. This is normal. Recalibrate, re-level, and try again.
Editor's Note: This is the second of a series of posts excerpted from Jason Griffey's Library Technology Report "3D Printers for Libraries."
Fused deposition modeling defines 3D printing for most people, as it’s by far the most common and in many ways the simplest technology for 3D printing. Fused deposition modeling uses a variety of plastics that fall within a range of melting points and that fuse when melted and resolidified, the most common of which are ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid). We’ll discuss the specifics of these and other print substrates below.
The most common arrangement for an FDM printer is called Cartesian print engine, because it uses basic Cartesian coordinates (X,Y,Z) to create the printed objects. Even this general category comprises multiple types of printers and two are most common: the Makerbot style, which relies on a fixed plane X and Y print head and moveable Z print bed; and the so-called “RepRap” style, which relies on a fixed plane X axis, while the Y axis is controlled by moving the print bed itself and the Z axis is accomplished by moving the entirety of the print head system vertically upwards.
Makerbot Replicator (above)
RepRap style 3-D Printer (above). Photo by John Abella.
Alternatively, with a Delta printer, a significantly different geometry for a FDM printer, the printhead is suspended from 3 arms that are controlled along vertical supports, while the print bed is completely stationary. This arrangement allows the printhead to “float” above the print bed and be located at any physical point in 3 dimensions simply by altering the relation of each of the three arms to the other. This is the same sort of control geometry in the flying cameras used in NFL games, applied to a robot.
SeeMeCNC's Rostock Max (above), a delta printer.
Regardless of the control geometry used, the method of printing is the same for both types of FDM printers. The printhead for both is a metal tube with a heating element and thermistor to control the temperature, and the plastic substrate is melted by the high heat of the printhead. Pressure is applied by forcing in more plastic, causing some of the liquid plastic to extrude through a small nozzle that ranges from .2-.5 mm in size.
A print from an FDM printer begins with a single layer of plastic applied very thinly to the print bed, the nozzle moving across the print bed and depositing said plastic in the shape of the object it’s creating. This initial layer is the base layer of the object, and the second layer will be deposited directly on top of the first, and will fuse due to the properties of the plastic involved. Once the second layer is completed, the third, fourth, and so on will follow, building the object over time along the Z axis. You can think of layer height as the equivalent of the DPI of a printed page. It’s the resolution of the object in the vertical dimension, and the smaller the layer height the smoother the final product will appear. It will also take significantly longer to print, since as you lower the layer height, you’re adding layers to the overall build.
For example, lets imagine you’re printing a 5 cm tall cube. If you print that cube at what would be considered a fairly rough layer height of .3mm, you’ll end up printing a total of 167 layers. If you printed that same cube at a fine resolution (for most printers around .1mm) then you’d end up printing 500 layers, tripling the number of overall layers and the time necessary to print the object.
Because FDM printers rely on building objects vertically in the open air, they have issues with specific geometries of objects, If you imagine an object being printed slowly from the bottom up, if the object has a significant overhang or free-hanging part like a wide doorway or something like a stalactite, it won’t be printable without supports on an FDM printer.
All FDM printer software has built in the ability to include supports for printing, when issues like this arise. Printing an object with supports means that the software builds in vertical towers whose only purpose is to give the object a structure upon which to print. The best case for a support structure is that it would be easily removable from the rest of the model, either by just peeling them apart or in a slightly more advanced process by printing supports in a type of plastic that is soluble in a solvent, while printing the object itself in a plastic that is insoluble. The most popular of these (discussed in next week’s post) is high impact polystyrene or HIPS, which allows a printer with dual extruders to print support structures that can be dissolved off of the actual print.
As with any sort of specialty product, a vocabulary of 3D printing has sprung up , and if you’re new to it, some terms are inscrutable without research. One example would be the two types of extruder setups found on FDM printers. The extruder is the part of the FDM printer that forces the plastic filament into the hot-end and through the nozzle onto the build plate. One is simply called a direct extruder, and the other is known as the Bowden extruder. On a direct extruder FDM printer, a motor on the moving print assembly includes the hot-end and the nozzle, and the motor pulls filament off the spool and drives it directly into the hot-end. The majority of FDM printers have a direct drive extruder. The Bowden extruder removes the motor assembly from the hot-end and nozzle, and takes it off the moving printhead altogether. In a Bowden setup, the motor pushes the filament from the spool through a tube connected to the hot-end and nozzle. The advantage to the Bowden is that it significantly reduces the weight of the moving print assembly, which means that it can move more quickly and can change directions without serious jitter problems. The disadvantage is that it is, in some sense, pushing a rope, and the more flexible the filament is the harder time the Bowden setup will have with pushing it into the print assembly.
A few other good-to-know FDM terms (and some of these I’ve already used without explaining, forgive me, dear reader) are: hot-end, build plate, nozzle, spool. The hot-end of an FDM printer is the metal piece with the heating element inside that melts the filament. Usually they are made of some form of non-reactive metal, such as aluminum, brass, or stainless steel. The nozzle is the very small diameter (.2-.5mm) that the melted plastic is forced through under pressure on its way to the build plate. There is a relationship between the nozzle diameter and the possible layer height of the output from the printer. Because you are extruding tubes of melted plastic, and they need to be pressed together in order to fuse, the layer height can’t be any larger than the diameter of the nozzle. If it were, you would be extruding into thin air, without the new layer pressing into the old layer. To help visualize this, if the width of your extruded plastic is .3mm, and you attempt to print at a .4mm layer height, there’s .1mm between the plastic and the layer below it...not good. In practice, a good rule of thumb is that the maximum layer height is somewhere between 75-80% of the nozzle diameter. So for a .4mm diameter nozzle, your maximum layer height would be around .3mm. Generally speaking, the goal is to have lower and lower print heights, as that makes for a smoother and smoother final product. But for rough prints, or demos, having a higher maximum layer height can speed up prints tremendously.
The last couple of FDM specific pieces of terminology are build plate and spool. Spool is easy, as it’s the way that filament is generally purchased and used. A typical purchase of ABS or PLA would be a kilogram (2.2 pounds) of plastic, wrapped onto a plastic or cardboard spool which hangs on the printer and plays out filament as needed. In an FDM printer, the build plate is the surface upon which the plastic is extruded. The specifics vary widely, but fall into a few basic categories, the primary of which is heated or non-heated. A heated build plate adds cost to the printer, but is absolutely necessary for printing certain types of filament (ABS, Nylon, and more).
Another aspect of the build plate is its composition, and whether you print directly onto the plate, some covering such as tape, or a glue or other adhesive. Heated build plates are usually made of either aluminum or tempered glass, although occasionally stainless steel shows up. Unheated build plates can be composed of the same things, as well as acrylic. The important thing with build plate construction is that you want something that will not warp or deform over time, since if the plate itself isn’t flat, it’s impossible to level it appropriately to the print heads. Glass is a very popular build plate material for this reason, although many FDM printers ship with alumninum plates that are then covered with a replaceable printing surface of some kind, most commonly PET tape or Kapton tape for a heated bed, or painter’s tape for a non-heated bed.
The price points for FDM printers are typically determined by size, more specifically print volume or the size of the print bed, and a variety of upgrades that makes feasible specific kinds of printing or the use of specific plastics. Print bed sizes range from very small (no more than 3 inches by 3 inches or so) to massive (over 12 inches by 12 inches). The print volume determines the maximum size of a single object that you can print, or conversely the number of smaller objects that you could print at the same time. Printing larger objects is also more difficult, because as you print larger things, there’s more opportunity for a small error to creep into the print due any number of common 3D printer issues.
Editor's Note: This is the first of a series of posts excerpted from Jason Griffey's Library Technology Report "3D Printers for Libraries."
The simplest way to understand a 3D printer works is to imagine it as a machine that makes bigger things out of smaller blocks. In some cases the “blocks” are a powder, in some they are melted plastic, or they may be a ultraviolet light sensitive resin, but always the process is large things being made from smaller substrates. A 3D printer is a simple sort of robot that understands how to manipulate the raw material it’s working with in three dimensions rather than just two, as an inkjet or laser printer does. This type of manufacturing is also called additive manufacturing, as opposed to more traditional subtractive manufacturing, where material is removed from a larger sample to create custom shapes in a process like milling, lathing, or CNC (computing numerical control) machines.
Imagine an inkjet printer that instead of printing ink extrudes hot plastic that cools quickly. Think of it like a hot glue gun where the plastic is solid, then gets heated to a liquid state, and then cools again into a solid. If it printed this plastic on a piece of paper, you’d end up with a slight raised design being “drawn” on the paper by the printhead moving back and forth across the paper (the X dimension) and the paper being moved through the print area (the Y dimension). Those of us old enough to remember the days when color printing was very expensive might recall hot wax printers that did basically this.
With a 3D printer, you add the last of the spacial dimensions, height, by moving the printhead and printing substrate (usually called the build platform in this case) apart from each other. In our inkjet analogy, imagine that you put the printhead on an elevator that could move it closer and farther away from the paper. If you do that while the printhead is putting down plastic, you can just keep them moving farther and farther apart, layer after layer, in the Z dimension. Over time, you end up with an object made of very thin layers of this plastic. That’s what most 3D printing is like.
This is the basis for almost all of the 3D printing that you have seen in media over the last few years, and almost all 3D printing that libraries have been involved with. Called fused deposition modeling, it isn’t the only type of 3D printing, just the most affordable.
In future posts in this series, I’ll describe other 3D printing types: selective laser sintering, stereolithography, laminated object manufacturing, and electron beam melting. While many of them are well beyond the means of most libraries, prices are likely to go down dramatically as soon as patents expire on the core technologies behind the printing methods. This is central reason that fused deposition became inexpensive so quickly during the past five years. Most people that follow 3D printing believe that laser sintering will follow suit shortly, as a key patent to that technology expired in January of 2014.
The next post in this series will be about the printing technology most central to libraries at the current time, fused deposition modeling, and then we’ll take a look at the other options that may be coming in the next 3-5 years.
Editors Note: This post is an excerpt from Improving the Visibility and Use of Digital Repositories Through SEO, by Kenning Arlitsch and Patrick S. OBrien. The authors, along with Montana State colleagues Jason Clark and Scott Young, will be teaching the online course/workshop Search Engine Optimization (SEO) for Libraries, which starts July 17.
Metadata schemas are powerful frameworks for organizing content, and libraries have long used them to describe their holdings (think MARC). Numerous schemas exist for academic disciplines: CDWA is used for art, Darwin Core for biology,
EML for ecology, DDI for social sciences, and so on. Dublin Core is probably the
most heavily used schema in digital libraries, and it is perfectly adequate for many
applications, but the problem with any metadata schema is that most website
developers don’t use any at all, and search engines can’t count on the metadata
being applied consistently in those that do. The result is that general-purpose
search engines like Google tend not to use the metadata even where it is applied
Some specialty engines, like Google Scholar, do make extensive use of metadata. Google Scholar, however, wants metadata schemas that can express bibliographic citations specifically and accurately, which Dublin Core does not do very well.
Because search engines crawl the web pages that are generated from databases (rather than crawling the databases themselves), your carefully applied metadata inside the database will not even be seen by search engines unless you write scripts
to display the metadata tags and their values in HTML meta tags. It is crucial to
understand that any metadata offered to search engines must be recognizable as
part of a schema and must be machine-readable, which is to say that the search
engine must be able to parse the metadata accurately. For example, if you enter
a bibliographic citation into a single metadata field, the search engine probably
won’t know how to distinguish the article title from the journal title, or the volume
from the issue number. In order for the search engine to read those citations
effectively each part of the citation must have its own field. Making sure metadata
is machine-readable requires patterns and consistency, which will also prepare it
for transformation to other schema. This is far more important than picking any
single metadata schema.
We invest a great deal of time and money creating digital collections, and we usually create web pages that describe the collection’s purpose, what it contains, its contributors, and so on, to give visitors some context they can use to understand
the collection. We also take great pains in creating metadata that describe each object in the collection to give it meaning and allow users to reference or discuss
the item. While humans can understand and associate the concepts they read,
search engines have a very limited capacity for interpreting the meaning of the
information we so painstakingly provide.
To help search engines understand the context and meaning of our digital objects we must provide structure to our content using additional tags in our HTML. These tags will say to search engines directly, for example, “this information
describes a specific digital object as a scholarly paper, written by an author who
works at an academic institution, published by an organization on a certain
date.” Sounds easy enough, but communicating with a machine requires an
up-front agreement on the specific language and precise vocabulary being used to
communicate. The word “bloody” has very different meanings to a person raised
in the United States and a person raised in the United Kingdom. Search engines
do not understand the regional variations, sarcasm, humor, hand gestures, facial
expressions, body language, tone of voice, inflection, and so on that humans rely
on heavily to communicate meaning.
Enter schema.org. In 2011 Google, Bing, Yandex (the largest Russian search engine), and Yahoo! “joined forces to create a common set of schemas for structureddata markup on web pages” with the aim of helping search engines to better
understand websites. Originally, schema.org was planned
to use only HTML microdata as the mechanism, or language for
implementing schema.org structured data vocabularies. But it has also recently
added support for RDFa as an alternative “language” that developers using “RDFbased
tools and Linked Data” can use to implement the schema.org vocabulary.
We think it’s important for repository managers (and especially catalogers) to be aware of these developments because they hold great promise for fulfilling the potential of the semantic web. Sites that already
offer microdata provide a great benefit to Google’s users through its “rich snippets,”
which display additional details about web pages in the search results.
Another example of Google’s use of microdata appears in its “recipe search,” where
metadata about recipes provide a faceted navigational search. If Google
can do this for recipes, imagine what it could do for library digital repositories that
already have rich metadata describing the objects. The bridge that will get that rich
metadata to be understood by search engines is the techniques recommended by
schema.org, and putting those techniques into place in digital repositories is the
responsibility of librarians and archivists.